Carey Price made 32 saves to record his fourth 0, at Air Canada Centre.
Mathieu Darche had a goal and an assist, while Erik Cole, Max Pacioretty, Rene Bourque and Lars Eller all scored. David Desharnais and Tomas Plekanec added two assists apiece for the Canadiens, who extended their winning streak to four games. Price was also credited with an assist.
Former Leafs captain Mats Sundin's No. 13 was retired in a pre-game ceremony, and the current version of the Leafs really could have used his offensive prowess.
Sundin is Toronto's all-time leader in goals (420) and points (987) and is sixth on the Maple Leafs' list in games played (981). The 40-year-old played his final NHL season with Vancouver in 2008-09 and he posted 564 goals and 1,349 points in 1,346 games with Toronto, Quebec and the Canucks.
After a scoreless first period, Montreal got the offense rolling with four tallies in the second period.
The Canadiens' first goal of the stanza came at 5:01 when Cole raced up the right wing with speed, cut to the slot and fired a shot high past Reimer.
Montreal made it 2-0 just under two minutes later after Bourque one-timed it home from the right circle off a perfect feed from Plekanec.
Pacioretty made it 3-0 at 15:54 with a power-play goal after he pounced on a big rebound in the slot off a point shot from P.K. Subban, and Eller capped the period with an explosive individual play.
Eller picked up the puck in the neutral zone off an errant drop pass. He gained the zone on the right wing and drove hard to the net on his backhand before switching to the forehand and sliding the puck past Reimer.
The Canadiens struck again just 1:29 into the final stanza when Plekanec hit Darche at the blue line while Toronto was in the midst of a line change. Darche went in alone and buried a quick wrister past the glove hand of Gustavsson to finish off the rout for Montreal.
Linesman Brad Kovachik worked his 1,000th career game...Montreal finished 1- for-2 with the man advantage, while Toronto failed to score on five power-play chances.