Jake Allen made 40 saves for Montreal (6-16-2), which fired Bergevin in the midst of one of the worst starts in its history after losing in the Stanley Cup Final to the Tampa Bay Lightning last season.
"I was surprised but obviously when we had a start like we did this year, you know, things [have] got to change," Canadiens forward Josh Anderson said. "It could be him, it could be players, and obviously they thought that they needed a little change-up in the organization."
It was the Canucks first regulation win in 19 games against the Canadiens dating to Oct. 27, 2015, and their first regulation win in 16 games in Montreal dating to Jan. 16, 2007.
"I like playing here, especially the fans," Pettersson said. "It's always a loud rink playing here. You've got a great fan base so it's always fun to play here. And I didn't know that fact, so it's good to break that."
Garland put the Canucks ahead 2-1 at 6:27 of the second period when he chipped the puck past Allen off a pass from Bo Horvat, who cut off Anderson's no-look pass attempt off the boards.