A ton of good cafes, after all its French isn't it? Not sure about veggie specific places, but I did have a veggie burger when at one of the cafes while my wife ordered meat in hers.

http://www.tourismemonttremblant.com/en/

Veggie on the mtn (in the village) is limited to the juice bar and some basic veggie burgers in the restaurants. Down in Saint Jolie (10k away) you might have better luck.

Tremblant has a ton to do.
-MTB trails are world class
-Fly fishing on La Diable is great
-Boat tours or SUP on the Lake?
-Hiking around the area has to be good
-there is a burly looking ropes course up on the MTN (never done it).

Have fun.

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USA Triathlon Level 3 Elite Coach
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The spa seems popular with the ladies.