You may have done the trip already.
No smoking anywhere in either airport. Those days are long gone. You would have to go outside which is easy enough to do. You will go through customs when you arrive so you can leave but will have to go back through security but you have lots of time. Montreal is a beautiful city. You do not indicate the time you are arriving? If during daytime, grab a cab/uber to Old Montreal for a few hours. If at night book the airport hotel, a Marriott or hit a lounge, you can pay a one time fee.
Toronto, book the hotel at Terminal 3. I am pretty sure it is a Sheraton.