Philadelphia (28-26-7), which has lost two in a row after a three-game winning streak and is seven points behind Carolina for the second wild card, will host the Pittsburgh Penguins in the 2019 Coors Light NHL Stadium Series at Lincoln Financial Field on Saturday.
Flyers rookie goalie Carter Hart was pulled in the first period after allowing three goals on nine shots for the second straight game (5-2 loss to the Tampa Bay Lightning on Tuesday).
"There's obviously a couple of bounces that didn't go my way, just like the other night," he said. "You look at these past two games and you put it behind you, but you learn from it. And I know it doesn't feel great right now, but you learn from it, you try to take the positives out of it and see what you can improve on, and just put it away."
Hart, making his fourth straight start, was relieved after Gallagher's second goal of the game made it 3-0 at 10:33 by Brian Elliott, who made 29 saves.
"We didn't give him a chance to even get in the game," Flyers coach Scott Gordon said of Hart. "The chances that we gave up right off the bat there, they were pretty good shots. And I'm sure knowing Carter he's going to say, 'I should have had them,' you know, 'I've got to make saves there,' and all of that. But at the end of the day, we can't give up those chances for the wrong reason."
Gallagher, who gave Montreal a 1-0 lead 58 seconds into the game, scored his third goal of the night, his Canadiens-leading 26th, at 2:56 of the second to make it 4-0.