There was just a bit of uncertainty heading into Tuesday's opening leg of Major League Soccer's all-Canadian Eastern Conference championship.

The Montreal Impact and Toronto FC are due to meet Tuesday night at historic Olympic Stadium, a 40-year-old Montreal landmark built for the 1976 Olympics.

Even though it's an indoor venue, a concern going into the match was the weather: The stadium roof is fragile — and snow was falling in the city Monday. But a stadium heating system appeared to be keeping any accumulation at bay and the Olympic Park announced the game would go on as planned.

The Impact normally play at Stade Saputo, which sits next door to the Olympic Stadium but seats just over 20,000. Nearly 60,000 are expected for the match.

The Impact has played games at the Big O, so the home-field advantage is still there, but the condition of the artificial turf — which lies atop concrete — might be a factor. Saputo's surface is natural grass.

"As far as the surface, of course, we would like to get to this point to such important games and playing the best possible conditions, but that's just one factor among many others in the game," Toronto star Sebastian Giovinco said.

Some of those other factors to consider for the two-legged MLS conference finals:

TORONTO VERSES MONTREAL

Montreal finished 11-11-12 in the regular season for the fifth seed in the East. The Impact defeated the New York Red Bulls 3-1 on aggregate in the conference semifinals to advance. They're led by Argentinian midfielder Ignacio Piatti, who scored 17 goals in the regular season and three in the playoffs.

The Impact appear to have gotten past the controversy involving former Chelsea star Didier Drogba, who lost his role as a starter to Matteo Mancosu. Drogba sat out of Montreal's second-to-last regular season match against Toronto, a 2-2 draw, because of the demotion. But he told reporters last week that he was focused on taking the Impact to the MLS Cup championship.

Toronto was the No. 3 seed in the East after going 14-9-11 in the regular season. TFC advanced to the conference finals with a 7-0 aggregate victory over New York City FC. The team is led by Giovinco, who has 21 total goals this season, including four in the postseason.

The Impact defeated Toronto in the knockout round of the playoffs last year.

"Last year was just a small taste," Toronto FC coach Greg Vanney said last week in a conference call with reporters. "We started extremely poorly in that game and paid for that, but I think it was just a taste of the rivalry continuing to build between these two franchises. It's a Montreal-Toronto rivalry in hockey and other sports that goes way, way back. We have enough guys on the roster from last year who remember that day and were embarrassed on that day, as was myself, but our mentality will be different than it was last year."

COLORADO VERSUS SEATTLE

The Sounders went 14-14-6 during the regular season for the No. 4 seed in the Western Conference. Seattle's story is the team's incredible rebound from last place in the conference and the dismissal of longtime coach Sigi Schmid. The interim tag was removed from coach Brian Schmetzer's title earlier this month. The Sounders, who defeated FC Dallas 4-2 on aggregate in the semifinals, are led by homegrown rookie Jordan Morris with 12 overall goals.

Colorado, which finished 15-6-13 in the regular season and narrowly missed out on the Supporters' Shield, got a knockout-round bye as the second seed in the West. Known more for their stout defense, the Rapids are led by Swiss forward Shkelzen Gashi with 10 goals in his first MLS season. The Rapids advanced after a penalty shootout with the Los Angeles Galaxy following a 1-1 semifinal.

Colorado won the MLS Cup in 2010.

Both teams have been stung by injuries this season. For the Sounders it was the unexpected loss of national team star Clint Dempsey because of a heart issue.

For the Rapids it has been the loss of goalkeeper Tim Howard, who had season-ending surgery Thursday after suffering a fracture of the right adductor longus in his groin while on duty with the U.S. national team.

Colorado will start Zac McMath, who lost the job when Howard joined the Rapids in July after 10 seasons with Everton in the English Premier League. McMath was one of the best goalkeepers in the league at 9-2-5 when Howard arrived.

"Credit to Zac for being very strong mentally, and prepared," Rapids coach Pablo Mastroeni said. "It takes a man to be able to take that information, given his performances, and not sulk and not throw his toy and not run out of the room and slam doors, to look at someone in the face and go, 'OK, this is your decision, all right. I'm a team player; I've got to respect that.'"