i haven't done exactly the same route, but done plenty of yvr - hkg routes that have similar time (one in the afternoon arriving in evening, one leaving in the early morning arriving around 6am)...
option a: you would force yourself not to sleep on flight.... that way you can probably sleep at the hotel at night
option b: force yourself to sleep on the plane.... but you would be arriving quite early in hk, can probably freshen up in the arrivals lounge before heading to the city
i guess it all depends on whether you can sleep well on the plane