The West side of Vancouver Island (Tofino, Ucluelet) is very nice. There's also the Gulf Islands and Sunshine coast if you want to stay in BC. I second the previous recommendation of the Oregon coast if you don't mind a little longer trip.
The east side of the Cascades is pretty hot in the summer compared to the coast so you might have a preference one way or the other.
Heading the other direction from the coast there's Glacier N.P. and Yellowstone which offer some great sights...