Upvote:24
The overriding answer that applies in all circumstances is "if you ask the airline to short check your bags you can get them at the layover point and then recheck them in again when you head off on the next leg." That is, you don't just hope that what the airline does automatically will be what is best for you, you request it.
A possibly useful thing to know is that when you go international-domestic in Canada, you usually have to clear customs (with your luggage) at the place you enter Canada, which in your case is Montreal, suggesting that the default would be ok for you, and you might not need to ask.
But a possible override to that is that since you're heading back out of Canada again there might be some cleverness to "save you the trouble" and check your bags all the way to your final destination. Might. Or might not.
So bottom line: ask the airline to do the thing you want.
Also, unsolicited advice: you don't need a whole cruise worth of suitcase to spend one night in a hotel. Put your toothbrushes, toothpaste, and change of undies/shirts in a carryon bag and try to interact with your checked luggage as little as humanly possible.