I cut a new key for my car for just $3. My friend did it for me. What she did is to go to the GM dealer and show the car registration paper (which is under my name).
You said you lost all the documents? I don't know if they would cut the key for you. But I am positive that if they cannot cut the key, they cannot change the lock.
I think there is a way to get a new registration paper. Mail to the SAAQ and said you lost the paper, ask they issue a new one. My friend did that. But now your friend is not in Canada...