We've been to Garde-Manger twice now so I feel like I have a pretty good take on the place. The gist of our take: good food, but sorely overpriced and the music is always too loud, to the point where you can barely hear yourself think.
As a vegetarian, the options for me there are incredibly limited. It's either a risotto ($32 for it with no meat) or a $14 tomato/avocado salad with fried cheese (expensive but very good).
Going down the whole menu everything seems grossly overpriced.. the main one being the Lobster poutine ($20)... the portion is way too small for that kind of price.
Expect to pay $50/person for a 2 course meal, without drinks.
The food is solid but I have a feeling Chuck's fame is adding too much perceived value to his restaurant, and for the price there are much better places to eat in Montreal, even in the Old Port area (DNA for example).
Worth trying once but after 2 times I don't think we'll go back for a long time..