" For example on my recent YYZ-YVR-SEA flight they wouldn't let me upgrade from H for the YYZ-YVR part because it wasn't transborder. But on the way home, she was all set to upgrade the YVR-YYZ part "yes, I can see you are transborder, you're just changing planes" but that was V (I don't know why) so I couldn't. (S'OK, I got a comp upgrade at the gate, it was a full plane.)"

If this is the case, they really blew it. You should have been able to upgrade with an H fare domestically, irrespective of the transborder segment. V is the lower fare from which transborder fliers can upgrade, not only the transborder segment but also the domestic segment. True, YVR-SEA has no Exec class to upgrade to, but if you paid that fare, you should have been permitted the upgrade, space available. Says so right on the certificate.