Nearly 70,000 spectators are expected for MLS Cup 2019 in Seattle, the first time the US city has hosted the title contest.
Seattle won the crown in 2016 at Toronto on penalties after playing to a goalless draw, Toronto's Justin Morrow missing in shootout and Seattle's Roman Torres netting the winner.
The Canadian squad avenged the loss in 2017 with a 2-0 home triumph, Jozy Altidore's goal in the 67th minute and an insurance marker four minutes into extra time by Victor Vazquez providing the difference.
Seattle defeated visiting Toronto 3-2 in an April regular-season meeting with Will Bruin scoring twice and Cristian Roldan adding another while Altidore scored twice for Toronto.
But Altidore has not played a moment of the playoffs due to a quadriceps injury.
"I still have to progress," Altidore said. "This type of injury is tricky. I'm trying my very best. I'm doing everything I can. I'm hoping to play some part in the game. I haven't played any soccer in a month, so that's where I'm at."
Toronto's top scorer this season has been Spanish midfielder Alejandro Pozuelo, who netted 12 goals and set up another dozen to spark the Canadian side, while Altidore contributed 11 goals and seven assists.
Pozuelo has adjusted his role in the absence of Altidore and provided a playoff sport.
"I've been playing as a false nine," Pozuelo said. "I kind of like that position because I can roam around and have the freedom to run in behind. But we know Jozy brings a lot of quality to the team. If he's not able to play on Sunday, I'll do my best to help the team."
The Sounders are strong in attack down the wings, which has been a weak spot for the Toronto defenders this season. Bu Toronto fullbacks have not played as far up in the playoffs as during the season, allowing them to better guard long passes, transition attacks and rivals playing out wide as Seattle likes to do.
Peruvian striker Raul Rudiaz led the Sounders in scoring with 11 goals and added three assists while US forward Jordan Morris had 10 goals and seven set-ups for Seattle. Uruguayan midfielder Nicolas Lodeiro had seven goals and 12 assists for the Sounders.
'A different Seattle'
Seattle defensive midfielder Cristian Roldan says the Sounders have learned some lessons from the finals loss two years ago.
"They ended up playing in a 4-4-2 diamond and we couldn't find too many answers. Tactically, made it very difficult for us to press, so you'll see that in this game," he said.
"(Seattle coach Brian) Schmetzer's side, he gives us a lot of freedom to play. You'll see a bit of that in this game. We're going to be on the front foot being at home in front of our fans, but you'll see a different Seattle than you've seen in the last two finals."
Seattle goalkeeper Stefan Frei ranked fourth in MLS with 116 saves and had a 1.44 goals-against average while Toronto's Quentin Westberg made 75 saves and had a 1.46 goals-against average.
Defending champion Atlanta United was eliminated by visiting Toronto 2-1 in the Eastern Conference final. Toronto beat visiting DC United 5-1 in extra time in the first round in Wayne Rooney's MLS swan song then downed host New York City FC 2-1 in an East semi-final.
Los Angeles FC, which captured the MLS Supporters Shield for having the best regular-season record, was ousted 3-1 by visiting Seattle in the Western Conference final. The host Sounders also eliminated Dallas 4-3 in extra time in the opening round and blanked Real Salt Lake 2-0 in a West semi-final.