I’ve boarded Canada-bound flights from the US without ever having my ID checked at the gate. I was under the impression that the burden of identification (for lack of a better, real term) lies with TSA in the US and airlines’ gate agents in Canada*. If so, then the AC GA displayed an even greater lack of judgment than one may safely assume.
*I realize that I have routinely had my ID checked at the gate when boarding AC flights in the US. However, at the time of the incident above, I sought the interpretation of someone familiar with airport procedures and the takeaway was “the only necessary ID check at US airports must occur at security screening by a TSA agent.” Take that as you may.