Originally Posted by
skofz
Also, can't do a *A upgrade on a codeshare flight. In OP's case, YVR-YUL should be upgradable if booked in Y/B, since it was ticketed under the AC flight number. But YUL-YVR (NZ codeshare flight number) would not be.
Not sure if the interpretation of the codeshare thing is correct. I suspect when on AC.com they say codeshares are not eligible what they really mean is that you can't get AC to upgrade you on a non-AC codeshare.
I would think the operating carrier probably could.