Can't happen, Vancouver Island is in the way for any wave to get big enough. Your best hope is an earthquake, we are loooong overdue for one of those. Maybe Mt Baker will erupt and Vancouver will be the new Pompeii, who knows. The point is, there are options.
Problem with the earthquake is that it'll also knock Seattle and Portland. Crap. That just makes the earthquake all the more attractive for you guys Also, as for volcanoes, Rainier's the one to watch, but that'll only fuck Seattle/Tacoma (not counting the plume of ash). St Helens doesn't count; it's in the sweet spot not to fuck over major metropolitan areas yet remains in their backyard. I actually saw St Helens venting as I was driving up I-205 in Portland back in 05/06. That was an amazing site, seeing a volcano erupting in front of you.