Morgan Rielly had a goal and two assists, and Marner and Michael Bunting each had two assists for the Maple Leafs (44-19-5), who have won four in a row and moved into a tie with the Tampa Bay Lightning for second place in the Atlantic Division.
Jack Campbell made 29 saves in his first start since a 6-4 win against the Seattle Kraken on March 8. He missed the past 10 games with a rib injury.
"I definitely felt like myself and just having fun and competing and playing my game," Campbell said. "There's obviously some details I have to keep clearing up, but I really liked the game from the boys in front of me, and I liked my game, so I just have to keep building from it."
"Just being healthy is huge. Everybody isn't always 100 percent, so it's a part of the game and it's a tough game. It was definitely nice to hit a reset button, work on some details and work hard in the gym. We have a wonderful staff, whether it's the medical team or the strength coaches to get me in good shape. It's just great to be back and competing again with the guys."
Ivan Provorov had two goals and an assist, and Kevin Hayes scored a goal and an assist for the Flyers (21-36-11), who have lost four straight. Carter Hart made 22 saves after missing one game with an undisclosed injury.
"We bent and we broke a little bit in the third period," Philadelphia coach Mike Yeo said. "Obviously, you have to try to make some plays and try to create but you have to make sure you are not feeding their transition and their rush game, and I just think we made more mistakes in the third period than they did. They have a lot of skill and they could capitalize on those."
Philadelphia defenseman Keith Yandle was a healthy scratch, ending his NHL-record consecutive games played streak at 989 games. He last missed a regular-season game on March 22, 2009, as a member of the Phoenix Coyotes.
Hayes gave the Flyers a 1-0 lead at 3:56 of the second period when he took a cross-crease pass from Provorov at the right post.