Thanks. Yes, I have seen the YVR connection navigator, which appears straightforward except that unless I am missing something, it gives no time estimate at all. (It refuses to load on my Mac with Chrome, Firefox, or Safari, but does work on my iPad.) I have been in some Canada Immigration queues (mostly in YYZ) that took more than half an hour, so some guidance there would be useful. If these particular queues are only for transit pax, I imagine they would go more quickly but it's not clear if that's the case.

gglave, I'm not sure what you are referring to by online check-in with AC -- if I have a seat assigment by phone, then the UA check-in agent will give me an AC boarding pass at SFO, right? (In which case I don't actually have to check in with AC, I can just go to the gate.) Or are you saying that AC will not give me a seat assignment by phone in advance?