VS premium seats out of MAN are just as rare to get as are the economy seats.
4 x a week LHR-YVR against BA & AC ? They would probably have more success on MAN-YVR where they would only be against Air Transat.
The MAN-YVR has always been massive right back to the Wardair days. Try getting a seat on TS or the previous TCX seasonal services - always full.(inc premium)