I'd have to agree with Busting Bladder. I'm up in Victoria, BC, and we share the same conditions.
You will want a drysuit or a 4:3 in summer and a 5:4 in winter. I think that a 3:2 with a vest would be too cold and would be a poor compromise.
I can't speak to the local Seattle spots, but the whole area is stunning. If you have the chance to come up and visit us in Victoria, BC, check out our local launch "Cook St" on a West. In the summer, Nitinaht Lake produces some of the smoothest wind in North America.
Also, you have to try the local WA, OR, and BC, brews