To answer my own question, using the Arrive Can App then passing through the Nexus machine was fastest.

We used it during COVID but the agent never even checked it at a land crossing; I think it was because we were having trouble getting it to appear on our phones.

In general, as a couple, do both have to have it on their phone? Can it be on one phone or paper? US Citizens flying into YUL.

Even though I never got COVID, I think I have COVID brain trying to remember that time.

Thanks in advance.

You don't need to have it on each phone (or any phone, for that matter). Just complete it and you're done. I often fill it out on behalf of my daughter when she flies, even if I'm not with her. The proof is when you scan your passport at the machine.

I filled out a for for me and my mom, but my plan is if they let my mom through Int'l connections I will enter Canada alone, can I still use the declaration that includes both of us?

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,"

I finally tried ArriveCAN redux on returning from a recent visit to the UK with my wife. I have Nexus but she doesn't. I reloaded the app, discovered my old account still worked and submitted the info for both of us. When we are both traveling there is a benefit but when traveling solo I'll stick with Nexus.