Why would it be a problem? I always do it. I never take Flight 7/3007 and 8/3008 all the way to YYZ because it results in less points. {They post it as a single YYZ-HKG segment}.
By doing this, AC allow the aircraft to pick up passenger on this flight in YVR and also operate it as one of the hourly flight between YVR and YYZ instead having to protect this flight and not let anyone on. CP used to make passenger change from a 747 {HKG-YVR} to a DC-10 or 767 or A320 for the YVR-YYZ segment. I would rather clear custom in YVR and continue on the 747!