Cole Caufield and David Savard scored, and Cayden Primeau made 23 saves for the Canadiens (25-31-11), who have lost four of five.
"Just keep going, I think," Caufield said. "We have spurts where we're really good. Just have to look at those things and find what we can do better. A lot of guys in this room want it a little bit more, and as long as we do that, we're headed in the right direction."
Montreal announced before the game that coach Martin St. Louis will be away from the team indefinitely because of family reasons. Assistant coach Trevor Letowski was behind the bench and will assume the head coaching duties for the time being.
"It was obviously different with ‘Marty’ not being here, but we have a great group in here, a lot of good coaches," Canadiens captain Nick Suzuki said. "It was business as usual. Obviously, missing him and hoping and wishing for the best for him."
Backlund put Calgary up 1-0 at 16:23 of the first period when he tipped Weegar's point shot past Primeau on a power play.
Backlund scored again 11 seconds into the second period to extend the lead to 2-0. He buried a no-look centering pass from Blake Coleman from below the goal line for his 200th NHL goal.
"It feels special scoring 200 goals, for sure, in this league," Backlund said. "I put in a lot of work in my life to get to the NHL, and to be able to score 200 goals is special. It took longer ... I got close there in early January, scoring 196 or 197 or something like that, and it seemed to take forever to get to 200. It feels really good to get it. It's special to get all the goals here in Calgary, too. Some good company here in the organization's history."
Martin Pospisil pushed it to 3-0 at 7:41 when he tapped a cross-crease pass from Jonathan Huberdeau over the goal line.
"I'm just trying to make plays out there," Huberdeau said. "I know fans want me to shoot. I can hear it from the crowd. That's what I do. It was nice. I think 'Pospi' had an empty net, so probably this one was good."