Well I was going to say don't believe the "how little rain" Seattle really gets, instead I'll let you decide. Basically there is very little difference between Vancouver and Seattle weather, we do get 7 more inches of rain a year.
Below are two web cams, one for Vancouver the other for Seattle, just check in on the Seattle one starting in about a week. Right now we have just moved out of monsoon rains into a good sunny period, influenced by the high generated over California which is pushing our usually nasty weather north. If it is sunny in Seattle, probably on average be sunny in Vancouver, we both get hit by the same weather systems.
Seattle Web Cam:
Vancouver Web Cam (Actually Simon Fraser University Web Cam but you can see Vancouver weather if you scroll down)
Most boaters here and in Seattle boat from May until the end of September, then the boats are basically prepared for our rainy season. If you plan to follow this pattern, then a traditional sailboat will fill your bill quite easily. If you are a cheap guy like me, wanting to get my money's worth out of the boat, you will want to extend your season of boating; this is where you will want greater protection from the elements.
Yes you can get canvas to surround your cockpit creating an extra "cool" room, however my experience is the canvas begins to fade, then get old, then need replacing. In Vancouver, to install this extra room including dodger, bimini and side canvas can cost up to $5,000 - and then years latter will need replacing. Getting an inside steering station, in whatever form the boat takes will be a much better investment. Most of my buddies who own a sailboat wish they had an inside steering station to extend there sailing season.
I've spent many many hours in the rain in the off season, sitting at the tiller while those below were having a great time - no fun.