Invitation V is probably the best place to have a laid back yet elegant vegan dinner in Montreal. The service is always fabulous and the fusion of flavours and cuisine is fantastic. My favourite dish which I've had many times is the "crab" cakes. Read more about them on my blog: http://mtlveg.com/2014/03/12/invitation-v-vegan-montreal/
Haven't tried their brunch yet but I really want to!