Yes, it might seem strange to you, but you should always tip the waiters in the province of Quebec. Usually, people leave at least 15% of the amount of the restaurant bill if you are satisfied with the service. Why? Because the waiters have to declare 15% of their sales as their salary to the government and are heavily taxed on it. Unfortunately for them, they are not allowed to demand it to their customers... So please, do not forget it, it's actually the biggest part of their salary.
In Quebec tipping is a way of life. Be nice and tip for good service.
If you don't speak French, ask the person first 'Do you speak English?' before asking them your question. In most touristy areas most people are bilingual, but not always.