Matthews and Mitchell Marner had a 2-on-0 in overtime but could not connect, with Marner's pass going past Matthews at the left side of the net at 2:50.
"I think we just overpassed it," Matthews said. "I wasn't really able to get my stick on it at the end. It's late in the game, late in overtime, a little fatigue setting in, but obviously would have liked to have seen that one go in the net, especially on a 2-on-0."
Danault tied it 2-2 with 52 seconds remaining in the third period and Allen pulled for an extra skater. He scored at the side of the net on a pass from Nick Suzuki, who had three assists and extended his point streak to six games (four goals, six assists).
The Canadiens trailed by two in the third period Saturday after scoring four straight goals for a 5-3 win against the Winnipeg Jets on Friday.
"I think we've been really resilient," Suzuki said. "Obviously we've been down in all the games, it's not something we're looking for, but it just shows a lot of character in the group that we have on the ice. And we're doing a great job of coming back and putting pressure on them (the Jets). I heard we're tied now with them, so it's going to be fun down the stretch."
Matthews put the Maple Leafs up 2-1 at 17:21 of the second period. Covered by Joel Edmundson in front of the net, he stuck out his stick to deflect Jake Muzzin's point shot downward for his fifth goal during a four-game goal streak.
Morgan Rielly gave the Maple Leafs a 1-0 lead at 4:07 of the first period with a wrist shot that went in off Montreal defenseman Ben Chiarot's leg while he battled Toronto forward Alex Galchenyuk in front of Allen.
Toffoli tied it 1-1 on the power play at 1:55 of the second. Suzuki's cross-ice pass froze Campbell and set up Toffoli to put a one-timer inside the left post.
"Obviously, we would have liked to have come out with the two points and not go into overtime," Matthews said. "We gave ourselves a chance but came up short. This one stings a bit, but [we're] moving on and we'll take our one point and go on to the next game."