After a long layoff of 16 days, the Major League Soccer playoffs will resume on Tuesday with the first leg of the Eastern and Western Conference finals. 

The opening match of the doubleheader will be played inside the Olympic Stadium in Montreal between Canadian rivals Montreal Impact and Toronto FC. 

The second contest features the best defensive team in MLS, the Colorado Rapids, against the dynamic Seattle Sounders led by attacking midfielder Nicolas Lodeiro.

The major plot twist in the Western Conference final is the appearance of Zac MacMath in the Colorado net after Tim Howard suffered an injury on duty with the United States men's national team. 

Below is a preview of both of Tuesday's contests in the MLS Cup play-offs. 

Toronto FC at Montreal Impact (Tuesday, 8 p.m. ET, ESPN) 

The Eastern Conference final is the biggest moment to date for Canadian soccer in MLS.

Toronto and Montreal are heated rivals in every other sport, and the two-legged showdown with a spot in the MLS Cup final on the line will bring a new element to the clash of prominent sports towns. 

"Each time we play these games they're more meaningful than the last," Toronto FC manager Greg Vanney said. "This rivalry continues to grow and become more exciting and more interesting for the fans." 

Instead of playing at Montreal's regular home field, Stade Saputo, the first leg was changed to the Olympic Stadium, where close to 60,000 fans are expected to be in attendance. 

"This is going to be special," Montreal midfielder Patrice Bernier said. "It’s great to see the crowd has responded and we’re able to fill the Big O with 60,000 people." 

“Soccer is the most beautiful and popular sport in the world and it deserves huge attendance, and we can only be more inspired by more people, so the more people, the better for us," Toronto forward Sebastian Giovinco said through a translator.  "It’s more exciting for everybody." 

The Reds are looking for revenge from last year's knockout-round game in which the Impact blitzed Toronto by a 3-0 score at Stade Saputo. 

"We have enough guys on the roster who remember last year, and we were embarrassed on that day," Vanney said. "Our mindset and mentality will be different than it was last year." 

In order to keep the hosts at bay inside the packed house in Montreal, the Reds have to keep Ignacio Piatti from creating a good amount of attacking opportunities. 

The goal for the Reds isn't just to stop Piatti when he's on the ball, it's also to have an eye on the Argentine a few steps before he makes his first touch. 

"For me, what sets him apart is his recognition in his craft to anticipate when transitions are going to happen and to be one step ahead of the opposition when those moments happen," Vanney said.

"For us, we have to be aware of him at all times, especially when we have possession of the ball, making sure that in those moments when he separates, we have a keen awareness of where he is. We have to be organized and aware of his surroundings." 

The same can be said for how the Impact have to mark Giovinco and Jozy Altidore in Toronto's quest for an away goal. The pair of forwards have been tremendous throughout the postseason for the Reds, who are looking to cash in on all their big investments from the last few years with an MLS Cup. 

One of the biggest battles will be waged in midfield between Toronto's Michael Bradley and Bernier. How the power struggle in midfield goes may depend on what formation the Reds utilize. Vanney has brought out the 3-5-2 in recent matches, but he also deploys a 4-4-2 diamond as well.

The Impact's tactics are pretty straightforward. Because of Piatti's technical ability, the Impact are a quick-strike team on the counter. They've also found a consistent scorer in Italian Matteo Mancosu, who bagged a brace in the knockout-round win over D.C. United. 

"He’s given us a different look up front in terms of his profile and quality," Montreal boss Mauro Biello said. "He’s been able to get in behind and constantly be in movement. These are all things that have benefited our team." 

There's a good chance this match won't end scoreless, which means the first goal could be critical in determining the pace of play. 

Colorado Rapids at Seattle Sounders (Tuesday, 10 p.m. ET, Fox Sports 1) 

MacMath has received a ton of attention since he was thrust into the starting role following Howard's injury against Mexico in CONCACAF World Cup qualifying. 

The Colorado netminder is no stranger to thriving between the pipes, as he earned six clean sheets in 17 matches before Howard arrived from Everton in July. 

"I think he’s proved that he’s a first-choice keeper in this league," Colorado head coach Pablo Mastroeni said. "He’s fantastic with his feet and great in distribution. He has a great goals-against average this year." 

"Zac’s familiar with the back line," Mastroeni continued. "He’s familiar with the group. This is not about individuals, this is about a collective effort and finding a way to beat Seattle." 

The team approach has helped the Rapids survive injuries during the season to Jermaine Jones, Shkelzen Gashi, Kevin Doyle and now Howard. 

The Rapids possess one of the most underrated midfield duos in the league in Sam Cronin and Michael Azira, while Axel Sjoberg is as good as they come at center-back. Add in Jones to the spine of the squad, and you have a side capable of silencing the dynamic Sounders. 

Lodeiro is the focal point of Colorado's defensive game plan. The Uruguayan scored four goals and contributed eight assists in 13 regular-season matches, and he's added a trio of postseason tallies. 

“The guys have played against the best forwards in the league week in and week out," MacMath said. "We have to continue to defend as a group and let the guys make decisions during the game that they think are best to help us keep a clean sheet in Seattle." 

Seattle's been on a meteoric rise since Brian Schmetzer took over for Sigi Schmid as manager. The Sounders were left for dead at the end of July, but they fought back to earn the fourth seed in the Western Conference. 

“Every game since we’ve taken over has been a must-win game," Schmetzer said. "Every single game we’ve had to this date has had a big meaning." 

In addition to Lodeiro in the playmaking role, the Sounders will need a strong performance out of midfield bulldog Osvaldo Alonso, who will be fighting to control the match through ferocious tackles and a possession-based game. 

Seattle also contains plenty of threats on set pieces, but they will have to deal with the 6'7" Sjoberg when they launch crosses into the box. 

"Nico’s delivery has been tremendous," Schmetzer said. "We know Colorado is the best team in the league defensively, and we will just go out there and play Seattle Sounders soccer. If we create enough opportunities, I think we have the quality to be able to finish one of those." 

Colorado won't sit back and defend for 90 minutes given the importance of the away goals in the series, but this match should be a little less open than the one in Montreal. A 1-0 final wouldn't be shocking. 

Joe Tansey covers MLS for Bleacher Report. You can follow him on Twitter; @JTansey90. 

Unless otherwise noted, all quotes obtained firsthand.

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