Interesting. Maybe things have changed, but last time I flew AC ex-YYZ to the US, which granted was last Oct., gate agent didn’t want anything to do with any checks, docs, attestation, nothing, except for the standard passport check at boarding. I used OLCI, and didn’t check a bag, so skipped check in counter. Even asked specifically when arriving at gate if they wanted to see proof of negative antigen test which was required at the time (was specifically told they don’t check for that, I agreed to the US attestation at check in, and that ‘they’ could spot check for proof though she hadn’t actually seen that happen, but when I asked who ‘they’ were that might conduct a check, she couldn’t answer that either).