Originally Posted by roadto17

Hi there - Story's a bit different as I was on one airline and one itinerary (not sure if yours is booked through one itinerary or two separate tickets - this might be the key question), but just did an International to US via YUL a few days ago. Didn't have any checked luggage, so can't help you there, but in terms of "entering" Canada - you shouldn't so long as you have BPs in hand for both segments. When you deplane, you will simply follow signs to "connections" and then they will form a separate lane for US connections. Scan your boarding pass, and get sent down to security and US immigration. No entrance into Canada.

ArriveCan wasn't necessary in my experience - I did not fill it out as was simply in transit (and the Federal government's ArriveCan page confirms this as well).

Just to confirm, the above was on one single itinerary where you are provided with both boarding passes upon initial checkin. If you aren't provided both BPs or are on two separate itineraries, your answer could well be different.

Good luck and safe travels!