How would the flights from LAX fit into the connection schedule? I think the a/c used on the LAX flights are 744s which would be more comfortable and quiet as the galley is to the rear of the cabin, and it's cheaper and less hassle to get to LAX than to YVR.

If you take an afternoon flight such as CX 839 from YVR, you'll get full meal services (lunch and snack/light dinner/supper) instead of a snack/light supper and breakfast on the late evening flights (CX 889 and the flights out of SFO). That might be a consideration.