If time is not a constraint than the food is well worth the wait if you're looking to enjoy excellent French cuisine for breakfast or lunch. I had the duck confit omelet and can easily say it was one of the best omelets I've had. It was cooked with brie and green apples, the flavors blended together very well. The side of baked potatoes complemented the dish perfectly.
Furthermore, L'Avenue has got the coolest bathrooms of any restaurant I've ever eaten at.
I definitely recommend this place to anyone looking for breakfast/lunch in Montreal, but not in a rush.