Originally Posted by Fly AA J all the way
So does that mean that if I was willing to spend the night in YVR, I could do my transcons in CX J for 45k miles? Wow, I can't wait till OW starts letting you do mileage upgrades on different OW airlines

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If you're originating in YVR, I don't see why you couldn't, assuming availability on CX, of course; no personal experience so perhaps someone else has done this or been denied. I don't think, however, that AA will route a USA-USA domestic flight through Canada. I know that Air Canada, for example, can't sell you BOS-xYYZ-SFO on a single ticket, I've tried.
Michael