Come to think of it though actually, the West coast presence for Asian-Americans is mostly driven by California -- the Pacific Northwest states probably don't seem to contribute that much to Asian-American population by sheer population, compared to California's sheer demographic weight (after all, it's the one US state larger in population size than all of Canada!).
I also kind of find it interesting that BC and California have so many of Asian descent (15-20%), but the states in between, Washington and Oregon, not so much with only single digit %'s. Portland isn't particularly evocative of Asian-Americans, with Seattle perhaps slightly more so, though both cities are seen as low in population of minorities broadly speaking. I'm guessing BC and California were favored as destinations but not so much in between? Perhaps it also means that the Asian-Canadian west-coasters didn't intermingle much with their stateside counterparts otherwise they'd be a more continuous distribution going north to south.