Originally Posted by
Sopwith
I wouldn't chance it. I did a similar US-Domestic connection last week. The problem is once you clear Canadian immigration, even with Nexus, you get kicked out to groundside and have to re-clear security and get to your gate.
Might be doable under ideal conditions, but a lot can go wrong to cause delays.
OP's wife would not need to do any of those things. Just minimal checks on passport/BP IIRC. I still wouldn't chance it because SFO-YYZ is delayed for me more often than not.
OP, is there no way to book one of the earlier flights out of SFO? UA will be flying that route and AC has flights at 7:35am and 9:55am which gives a nicer buffer than 12:00pm.