This is a Heerman's gull, in my opinion among the handsomest of a somewhat disrespected group of birds (i.e., "seagulls").
This species occurs in relatively small numbers throughout summer and fall in southern BC, most commonly along the west coast of Vancouver Island. It breeds in Mexico.
The picture above was taken near Carmel, California. It's a somewhat odd picture; for some reason it looks like an old-fashioned museum diorama with a stuffed bird in the foreground. It was a nice spot though, with sea otters bouncing around in the surf.