US-CAN-US-XXX routing legality?
 

What's the legality of a one-way outing like the above scenario, ex. ORD-YVR-SFO-TPE? Obviously this is with ORD-SFO not having award availability the day I need. I know ORD-YVR-SFO is not allowed as a standalone, but is that the case even if continuing on internationally?

I've never had a problem booking it.

Just don't talk to any agents at the airport until you're in SFO.

Who are the operating airlines? If either of the transborder segments are UA, there should be no issue.

Technically speaking I don't even think that's necessary, since you're being transported from the US to TPE, which is perfectly valid for any airline to do.

But again, I wouldn't expect agents to know the rules. In fact, I have ample experience with them overreacting to things that are allowed.

Even if the operating airline made a difference (and I stand by my assertion that it does not), you need the agent to understand that.

So just don't talk to anyone until you're in SFO regardless of what you do, or expect a hassle at check-in. Though best-case scenario would be a rebooking onto ORD-SFO non-stop, which I almost had in BOS once (had it not been for the J0 Y0 inventory of all the flights...)

I think it's only the start and end airports that matter, the number of connections and their location is irrelevant.

The airline has sold you a ticket from A to B, the number and place of the connections is a convenience for the airline and is not guaranteed. All the airline has is a contract to get you from A to B, how they do it is changeable by the airline at their discretion.

This is with both ORD-YVR and YVR-SFO on Air Canada.