And then there were two.

After a pair of major upsets in the conference finals, MLS Cup will again be contested by the Seattle Sounders and Toronto FC on Sunday at CenturyLink Field (3 p.m. ET; ABC/ESPN 3 | Tickets).

According to FiveThirtyEight's SPI, the Sounders are a 65% favorite to win it all on Sunday and are fancied by the sportsbooks, too (-210 Seattle, +185 Toronto). But you can't always trust the numbers. Here's everything you need to know heading into Sunday's final.

Backstory: It's deja vu all over again. For the third time in four seasons, these two teams square off for MLS' biggest showpiece. The previous two meetings occurred at Toronto's BMO Field, with Seattle winning in a penalty shootout after a 0-0 draw in 2016 and Toronto winning 2-0 in 2017. There's a fair bit of history among the players themselves, too: 10 of the TFC and Seattle players in this year's postseason also appeared in their previous two finals: six from the Sounders (Nicolás Lodeiro, Cristian Roldan, Jordan Morris, Joevin Jones, Román Torres, Stefan Frei) and four from Toronto (Michael Bradley, Justin Morrow, Jonathan Osorio, Drew Moor).

These two have met plenty outside the playoffs, too. In their all-time head-to-head series, Seattle has won nine of the 14 regular season meetings.

Playoff path: It's fair to say that the East's No.4 seed and the No.2 team in the West have had a serious journey this postseason. With a revamped playoff schedule and the added tension of a single-elimination format, both teams arrive at Sunday's final with some miles in their legs. They both emerged from the first round and coincidentally, both needed extra time to do it.

Seattle survived a wild affair with FC Dallas, 4-3, before rolling to a 2-0 victory against Real Salt Lake in the conference semifinal and an enormously impressive 3-1 win at Supporters' Shield-winning LAFC in the conference final. They not only managed to nullify 2019 MLS MVP Carlos Vela at the Banc of California stadium, but scored with three of their five shots on target. Economical, to say the least.

As for Toronto FC, they scored a whopping four goals in extra time to overcome Wayne Rooney and DC United 5-1 in the first round before edging top seed New York City FC 2-1 in the conference semifinal thanks to a late penalty from Alejandro Pozuelo. (The foul by Ronald Matarrita was so inexplicable and so unnecessary that he should almost be credited with an assist.) The Canadians played the upset card again in downing reigning champions Atlanta United 2-1 in the conference final via a late, outside-the-box golazo from substitute Nick DeLeon -- don't let him shoot from range, Seattle, as as three of his six playoff goals have been launched from beyond the penalty area -- and leaving the near-70,000 in Mercedes-Benz Arena sitting in stunned silence.

Connecting thread: As mentioned above, this is the third MLS Cup meeting between the two in four years, but perhaps providing a bigger hint of what's to come Sunday was their lone regular-season meeting earlier this season, in which Seattle overcame a Jozy Altidore brace to win 3-2 at home at CenturyLink Field.

Another thread running between these storied foes is Sounders goalkeeper Stefan Frei. He was traded from TFC to Seattle back in December, 2013 and has been an institution between the posts in the Pacific Northwest ever since. Frei has played in 13 postseason wins since then, the most in MLS over the past six seasons. The only other players with more than 10 wins over that span are fellow Sounders Cristian Roldan (12) and Nicolas Lodeiro (11). Could his experience prove crucial in settling Sunday's contest?

Tactical contrast: It will be a genuine chess game considering that both sides leaned heavily on strong defensive and counterattacking performances to reach this point. In short, they can't both sit deep and wait for the other team to make a move: soccer's come a long way from its days getting skewered by The Simpsons. With Seattle playing at home and having full use of its stable of attackers -- unlike TFC, who might be without Jozy Altidore -- the feeling is that Seattle will be the more aggressive of the two and leverage its flying full-backs to spread open the TFC defense. Still, TFC are a team that likes to press and can use that tactic to slow down the Sounders' midfield.

Headache: At this stage, one would be hard-pressed to think of a selection headache for Seattle. The XI that took the field in Los Angeles will likely take the field again Sunday against TFC. The only potential foreseeable change could be at center-back if coach Brian Schmetzer feels like restoring Roman Torres in place of Xavier Arreaga to add experience and a bit more muscle.

One thing that might be a no-brainer is continuing with the winning combo of Lodeiro and Raul Ruidiaz. (More on both of them in a minute). According to Elias Sports Bureau, the Sounders are 21-5-4 (regular season) and 4-1-0 (postseason) when these two are in the starting lineup together.

The big question for Toronto FC boss Greg Vanney is the status of Altidore. If the big man is 100 percent, you have to think he'll get the start, though Nicolas Benezet and Richie Laryea have shown in this postseason that they can help fill the goal-scoring duties.

Star man: It seems like Seattle has a different star man each match. Against FC Dallas, it was Jordan Morris; Lodeiro stepped up against Real Salt Lake and Ruidiaz was the star in toppling consensus favorite LAFC. In this case, we will continue with the Peruvian striker, whose big game pedigree is beyond reproach: four postseason games, four goals and three assists.

Overall, Ruidiaz has been a revelation for the Sounders. His six playoff goals since joining the team at the end of June, 2018. Not only has that pulled him level with Clint Dempsey for No.2 on Seattle's all-time playoff scoring chart, but he's tied for second-most goals in a player's first five MLS postseason games behind LA Galaxy legend Carlos Ruiz (seven).

Despite a more discrete performance against Atlanta United, Alejandro Pozuelo is still the main man in red, and he will relish the challenge of playing spoiler in attack. His 12 goal, 12 assist season made him just one of four players to break double digits in both categories in 2019, with Vela the only one with more than 12 in both categories. He's also scored twice and assisted twice in the playoffs, making him TFC's most potent threat.

Where the game will be won or lost: Seattle took advantage of a soft LAFC midfield to put Bob Bradley's men to the sword. TFC's midfield trio of Michael Bradley, Jonathan Osorio and Marky Delgado aren't afraid to get nasty, so chances are it will come down to whether Seattle can handle and beat the TFC press in midfield.

X factor: If Seattle find themselves struggling in the second half and are in need of a goal, Victor Rodriguez is a pretty nice playmaking option to have coming off the bench.

TFC's penchant for big goals off the bench or from unheralded players is remarkable, with the likes of Benezet, Laryea and DeLeon scoring massive goals, so it would be no surprise if Patrick Mullins or Tsubasa Endoh somehow tilts things in TFC's favor.

This could also be a spot where home field advantage factors in. Toronto has only won in two of its eight all-time visits to the west coast. The last time they did it? A 1-0 victory decided by Jozy Altidore's penalty on May 6, 2017. That said, they have the third-best record away from home in MLS this season, picking up six wins and seven draws in 19 games. Only conference champions LAFC and NYCFC managed more, but they're watching the remainder of the playoffs at home.

Toronto FC will win because: Unbeaten in their past 13 MLS matches, TFC have become a team of destiny, with contributions from almost everyone on the squad. That confidence and belief will bear out in Seattle to complete an unlikely Cup conquest.

Seattle will win because: Buoyed by their boisterous crowd, the Seattle attacking trio of Ruidiaz, Morris and Lodeiro will overwhelm TFC's defense in the second half to lift the trophy. If they can break the game open in the first half, even better: the Sounders are 12-0-0 when leading at the break this season, including in the playoffs.

Prediction: Seattle 3-2 Toronto. The 2019 postseason has been the highest scoring in MLS history, with a current average of 4.1 goals per game, so we'd expect this game to bring the fireworks rather than offering up another tight, tense affair decided by a solitary strike.