Report back from YUL. Forgot about ArriveCAN until we were on the ground at Montreal. Downloaded the app, and it turned out it still recognized my email address from years ago just had to reset the password. My info including both traveller's passport numbers were still there. Answered the questions and saved;all while taxing to the gate.

It did save time having to answer using the machine that you scan your passport at which could but you a bit ahead going to the next steps.

Basically the same experience as allbrosca:
"My recollection is that I answered my questions online, scanned my passport, got a receipt, showed it to agent on way out. He did not ask a question. Handed it in on way out of baggage hall,"