Even if it is AC - CP or CX CNX at YVR, there is no problem with interlining. Even if they can't issue boarding passes at YEG, they can certainly tag the bags.
As for travelling YVR - HKG in Y, I would avoid both CP and CX. The 340 is a much more comfortable aircraft in Y because it is only 8 abreast.
That being said, stick with CP. Don't run the risk that CP is pulled out of OW before you fly. Although there is usually a warning of six-months or so, there are no guarantees in these cases.