Schenn scored his first NHL goal in the first period, which gives him something to bring to the table when the Maple Leafs' veterans dine at the rookies' expense when the team continues its four-game trip in South Florida.
"It's going to be an expensive one, but when you get the rookie dinner in the NHL that means you've made it, so it's going to be an honor to pay for it," said Shenn, the 19-year-old rookie defenseman who opened the scoring 14:37 into his 41st game.
Nikolai Kulemin restored Toronto's one-goal lead with his eighth goal early in the second.
Blake scored 3:07 into the third to put Toronto up by two. He made it 4-1 when he beat Carey Price at 9:13 for his 19th goal of the season, and second within 6:06.
Jeff Finger scored Toronto's fifth goal with 1:04 remaining in the third as the Maple Leafs evened the season series between the rivals at two wins apiece.
Toronto, which lost 5-0 in Buffalo on Wednesday, improved to 3-1-1 in its last five games.
"We didn't really like our outing last time in Buffalo and playing in Montreal the rivalry speaks for itself, but I think overall as a team we're trying to get some wins here," Blake said. "We're not a San Jose/Detroit type team. In order for us to win we've got to play the way we can play and that's use our speed, make the simple plays and get on the forecheck and shoot the puck, and I thought it was just a great team effort tonight."
Toskala, who entered with a 3.34 goals-against-average and an .883 save percentage, was singled out for criticism earlier this week by GM Brian Burke and coach Ron Wilson.
"That was the fifth game in a row I got points, so I'm pretty happy with that," said Toskala, 3-0-2 in his last five starts despite allowing 17 goals during that span.
Canadiens captain Saku Koivu believes the team's upcoming six-game road trip will provide an opportunity to recover the form that has led them to 64 points through 53 games, still good enough for second place in the Northeast Division -- 15 ahead of fourth-place Toronto -- and fourth overall in the Eastern Conference.
"It's time to get some bonding time and spend some time together," Koivu said. "Sometimes it's easier to really be simple and do your things and get that focus back when you're on the road and away from all the distractions."
Maple Leafs defenseman Mike Van Ryn went to the dressing room 4:41 into the second, shortly after he was driven awkwardly into the boards by Montreal's Max Pacioretty, who was called for charging on the play at 2:47.
"I'm sure that's a 5-minute [major penalty]," Wilson said. "He'll be out for a while. The ref said he wasn't injured. I said I encourage our guys to get up if they're hurt. Unfortunately, the ref thought he wasn't hurt. This hitting from behind stuff, they've got to fix that."
Van Ryn, who did not return, has missed a total of 29 games to injury this season, including an 11-game stretch following a 6-3 win over the Canadiens on Nov. 8, a game he left after sustaining a concussion when he was checked into the boards from behind by Kostopoulos.
"When I saw that I could have hit him from behind I really gave up a little bit there, so it's a call the ref probably has to make but there was no intention there to hit him like that," Pacioretty said.
After Blake's two third-period goals increased Toronto's lead to 4-1, Kostopoulos drew Montreal within two when he lunged along the ice to swat in a loose puck at the left edge of the crease at 11:02.
Price, who made 36 saves, started in place of backup Jaroslav Halak, who fell ill before the game.
"It doesn't really matter, you know, you prepare the same way anyway," Price said. "You've got to be ready to play no matter what."
Toronto enjoyed an 18-5 margin in shots in the opening period.
Chosen fifth overall by the Maple Leafs last summer, Schenn beat Price with a shot from the outside edge of the right faceoff circle.
The goal came just 20 seconds after referee Eric Furlatt disallowed an apparent goal by Kulemin. A video review supported Furlatt's ruling that Kulemin's stick made contact with the puck above the height of the crossbar when he tapped a rebound of Pavel Kubina's shot out of midair and into the net at 14:17.
D'Agostini scored his ninth goal on a two-man advantage 25 seconds into the second.
Kulemin restored Toronto's one-goal lead when he beat Price from the slot at 2:37.
Montreal held a 15-5 shot advantage in the second, but was outshot 41-33 overall.