Wish I could book them right now og - from all your comments it's going to be Cathay - but have to wait for the seats to be available - flying December 15 2014 hoping to return by December 30. I think seats will be released around Christmas Eve/Christmas Day perhaps for booking.
It seems there is no problem when you search the entire journey with return - but when doing them separately the avails change (when using sample date). We have to book the journey across and then wait for the return dates otherwise we may miss out altogether, so taking a chance we can get the full journey.
First plan is Per-HKG-Vancouver. It truly is a long haul but don't think we can separate the legs for a stopover as the options are removed when you try that search.