I see you no longer have to get your bags and take them through customs from your original flight when you travel to the US in Toronto, I was wondering if this is true in Montreal as well.
Actually, whether you do or not in Toronto depends on the airline. The last time I flew Air Canada the bags automagically transfer and in most cases you don't actually have to handle them during your transfer in TO; West Jet we had to claim our bags from a special area and take them into the US Customs area and put them on the belt.
If your flight originated in Canada and you have a boarding pass for a connecting flight to a U.S. destination, you must follow the U.S. Connections signs, go through pre-boarding screening checkpoint “C”, and then go through U.S. Customs. Your checked luggage will be transferred automatically by the luggage-handling system. Note, however, that U.S. customs officers are authorized to recall your luggage, if necessary, for manual inspection. If the customs officers do not yet have the information on your luggage at hand, you will be asked to proceed to the waiting area.
FWIW, I always check with the airline agent when I am checking in re: what will happen to my bags and will I have to transfer them myself. Although I may know what to expect, I prefer to be told again in case something has changed at the last minute.
Montreal was the pilot for the check through baggage and had the system several years before Toronto. Toronto still only has it at T-1 (Air Canada) T-3 you still have to collect your bags.