Valeri Nichushkin had a goal and two assists, Nathan MacKinnon and Mikko Rantanen each had a goal and an assist, and Makar had three assists for the Avalanche (37-22-6), who led 4-0 in the first period and have won three of four. Alexandar Georgiev made 15 saves.
Colorado, which was 3-for-3 on the power play, moved within four points of the Minnesota Wild, who have played two more games, for second in the Central Division.
"That's exactly how we would have liked to start," Avalanche forward Logan O'Connor said. "I think we didn't end the game on the right note; for example, we thought we could have been a little tighter and better in the third period. But we're definitely happy with the win overall to start this four-game road trip off."
Josh Anderson had a goal and an assist, and Nick Suzuki had two assists for the Canadiens (26-35-6), who have lost seven straight (0-5-2).
"They have so much motion and movement," Montreal coach Martin St. Louis said. "It's positionless offense and it can get very confusing, and I think we just got away from how we want to defend that. We were just so preoccupied with the movement instead of sticking to how we're supposed to defend it.
"And I definitely saw improvement, so we used the next two periods, especially the third, to try to correct ourselves a little bit and learn from it."
Jake Allen allowed six goals on 15 shots and was replaced by Sam Montembeault after J.T. Compher gave Colorado a 6-1 lead at 3:58 of the second. Montembeault made 16 saves in relief.
"Jake's not to blame," Canadiens defenseman David Savard said. "We played poorly in front of him. We left him on his own. It's very disappointing after all he has done for us this season."
Lehkonen put the Avalanche ahead 1-0 at 2:59 of the first period after deflecting O'Connor's wrist shot from the top of the left face-off circle.
Bowen Byram made it 2-0 at 6:09 when he skated around Montreal defenseman Kaiden Guhle and cut across the goalmouth before reaching around Allen's pads to score.