The 29-year-old defenseman scored 10 points (one goal, nine assists) in 24 games and can become an unrestricted free agent after the season.
"I've been watching them now since I got traded … they're playing really well right now and it's a good D corps in Montreal right now," Gustafsson said Wednesday. "It's going to be fun to be a part of that. I'm just going to take it step by step here and see how it goes. But I'm really happy to be a part of this organization."
A fourth-round pick (No. 93) by the Edmonton Oilers in the 2012 NHL Draft, Gustafsson has scored 129 points (29 goals, 100 assists) in 245 regular-season games with the Flyers, Calgary Flames and Chicago Blackhawks, and has five assists in 15 Stanley Cup Playoff games.
"Not so long ago, Gustafsson had 60 points (2018-19 with Chicago), 17 goals," Canadiens general manager Marc Bergevin said. "He's a player who moves the puck well and can help us on the power play."
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Gustafsson said he thinks he can get back to the level he played at two seasons ago with the Blackhawks.
"Yes I can," he said. "I want to be that guy, I want to be come back to that guy I was. I think in Montreal I can be that guy. I think the team in Montreal is very good, they have good all-around players and I'm just happy to be a part of that team. This is going to be fun to see how far we can go here."
The Canadiens acquired defenseman Jon Merrill in a trade Sunday from the Detroit Red Wings for forward prospect Hayden Verbeek and a fifth-round pick in the 2021 NHL Draft.
"They're very different players who bring a different aspect to our lineup defensively," Bergevin said about Gustafsson and Merrill.
Defenseman Victor Mete was placed on waivers Sunday by Montreal and claimed by the Ottawa Senators on Monday.
The Flyers also traded forward Michael Raffl to the Washington Capitals on Monday for a fifth-round pick in the 2021 draft.
Montreal (18-12-9) is fourth in the seven-team Scotia North Division, six points ahead of the fifth-place Calgary Flames.
Philadelphia (19-17-6) is sixth in the eight-team MassMutual East Division, six points behind the fourth-place Boston Bruins.
The top four teams in each division will qualify for the playoffs.
NHL.com columnist Dave Stubbs contributed to this report
