The best-of-7 series will be decided in Game 7 at Boston on Tuesday.
"When the season is on the line, you want to play hard, you want to leave it all out there," Marchand said. "Sometimes it bounces your way, sometimes it doesn't. Luckily today it bounced our way. Again, though, we're fighting for our season now, next game, we don't know how it's going to play out, but we're going to have fun doing it."
WATCH: [All Bruins vs. Maple Leafs Game 6 highlights | Complete series coverage]
Jake DeBrusk and Torey Krug scored, and Tuukka Rask made 22 saves for the Bruins.
"To me this is the best we've played," Boston coach Bruce Cassidy said. "We kind of knew we had to step up. Today was more the way we wanted to play, we wanted to be aggressive keeping pucks alive with our defensemen. I thought we were attacking the net better, just more overall of our identity. Obviously we were desperate, but this is the kind of thing we talked about on Saturday about trying to hit our ceiling."