I'm gonna be in Montreal for a few days but my carrier doesn't provide any service. Is there any Canadian carrier who sells a sim card just for data for a few days? I'm used to the European easiness of buying sim cards.
I found two options, indicating it's at least possible for a moderate price:
I can't claim that it's factual and current, but it's certainly thorough. This wiki has a lot of information on prepaid sim cards in Canada.