The Maple Leafs lead the Edmonton Oilers, who have two games in hand, by seven points for first place in the Scotia North Division. The top four teams will qualify for the playoffs.
"The guys have worked hard through a very challenging and unique season," Maple Leafs coach Sheldon Keefe said. "I think you do have to acknowledge that we spoke about it before the game, about let's get it done here tonight. We acknowledged that after the game, but we also have acknowledged that we're working towards bigger things.
"It's a nice accomplishment, but we're going to be continuing to work towards building our team to be ready to play when it counts the most."
Auston Matthews scored his NHL-leading 35th goal, and Jack Campbell made 32 saves for Toronto (31-13-5), which has won three in a row after losing its previous five.
Joe Thornton got his 1,100th assist, becoming the seventh player in NHL history to reach the milestone, and Jason Spezza had two assists to tie Maurice Richard for 99th in points in NHL history (966).
"We're playing with a couple of living legends," Matthews said. "It's pretty awesome at this stage in their career how passionate they are about the team, about winning, about performing every night. … It's been awesome to have [Spezza] here for the second year and play with a guy like 'Jumbo,' two guys that have a lot of history in this game. To witness them accomplish what they've accomplished, obviously, tonight was a big night for both of them."
Nick Suzuki scored, and Jake Allen made 25 saves for Montreal (21-18-9), which has lost three of its past four games and remained six points ahead of the Calgary Flames for fourth in the division.
"If you look at the games that we've played against them, they've been really close games," Canadiens forward Josh Anderson said. "And a lot of those games I do believe we were the better team. But then again, we just got to work on some of those mistakes and correct those down the road.
"But like I said from Day One, I believe in this team, and we've got a great group of guys in there and we can do some really good things. We've just got to put it on the ice and get through this together."