If I read the OP correctly (and I'm not sure I am) it sounds like the question may be related to a connecting leg on this itinerary. If this is entirely one itinerary, Philippine Airlines connecting to AA, then an AA domestic US / Canada connecting segment will be considered part of the overall international journey. So a 70 pound bag would be accepted, with the fees that 3Cforme referenced.

If you have purchased two completely separate tickets, one on Philippine Airlines and one on AA, then I don't know if you could get away with a 70 pound bag since AA doesn't know about the international leg.