Here are three storylines that will help determine which side lifts the trophy when today is done.
Looking out for Jordan Morris
Toronto FC's backline got exposed a fair bit against the Montreal Impact, something overshadowed by the dramatic narratives that swept Toronto to the final. The back three of Nick Hagglund, Eriq Zavaleta and Drew Moor will have to be much improved today if they want to win. There is no second leg to save Toronto FC from a slow start this time around.
A major key to that success will be shutting down Seattle rookie phenom Jordan Morris. The striker is fleet of foot and good at getting behind attackers, the exact kind of forward that plagued Toronto FC against the Impact last round. Not only that, but Morris has some of the best midfielders in the league playing balls into him.
Bradley vs. Lodeiro
Speaking of quality midfielders, two will be crucial to today's match, and how they interact with one another. Michael Bradley has been central to everything Toronto has accomplished in these playoffs, and that will not change today. He will likely be tasked with keeping an eye on the centre-piece of the Seattle squad: Nico Lodeiro.
The Uruguayan international turned Seattle's season around when he was acquired from Boca Juniors and is among the best playmakers in the league. Michael Bradley will try to tangle the strings he likes to pull during the match, just as he has with many of the other star midfielders Toronto has faced this season.
The Unexpected Hero
As much ink, voice and air time that has been devoted to talking about MLS Cup this week, what happens when these two teams take to the field today is just a guess at this point. Rarely, if ever, does it play out as expected. All the talk in Toronto is surrounding Sebastian Giovinco, Bradley, and Jozy Altidore, while Seattle's talking point revolve around Lodeiro, Morris and Ex-TFC keeper Stefan Frei.
But in a one-game scenario, it is just as likely that one of the secondary players takes over and steals headlines. After all, it was Hagglund, Armando Cooper and Benoit Cheyrou who each scored their first goal of the season in the second leg against Montreal to get Toronto to this point.
Toronto FC: Irwin; Zavaleta, Moor, Hagglund; Beitashour, Cooper, Bradley, Osorio, Morrow; Altidore, Giovinco.
Subs: Bono, Bloom, Williams, Cheyrou, Johnson, Endoh, Ricketts.
Seattle Sounders: Frei; Mears, Torres, Marshall, Jones; Alonso, Roldan; Lodeiro, Friberg, Morris; Valdez.
Subs: Miller, Scott, Fisher, Evans, Fernandez, Ivanschitz, Gomez.
Venue: BMO Field Toronto, ON
Kickoff: 8:00 p.m. Eastern
SB Nation Opposition Blog: Sounder at Heart
TV: TSN, FOX
Radio: TSN 1050
Streaming: TSN Go App