If you are not camping, please be aware that motels are often filled - especially on weekends in the San Juans, around Puget Sound, and along the north Oregon coast. It's a beautiful cycling route - but also very popular with all those city folk from Vancouver, Seattle, Tacoma, and Portland - all of which are no more than an hour from the coast. If you are willing to do hostels - check out hostels.com - some also take reservations, but I hate having to keep to a fixed schedule while touring. After Labor Day (that's Labour for you blokes) - 1st weekend in September - things open up and rates go down a little. Make advance reservations for that weekend.
If you haven't ruled out camping completely, I would highly recommend for this tour since Washington, Oregon, and California all have great state parks with hiker/biker campsites. Many people touring the coast choose to camp but stay in a hostel every third or fourth night. You carry more weight, but you get the best of both worlds since motels tend to be clustered in ticky-tack strips.
One of my favorite places is Cathlamet on the Columbia River - halfway between Portland and Astoria - it's an old logging/fishing/dairy town that hasn't yet been "discovered" - you can cross the river on a ferry here - or head downriver thru the Skamokawa wildlife refuge. By the way - Cathlamet rhymes with an oath more extreme than "Gosh-DARN-It" - that goes for Willamette, too - you are a dead give-away of a tourist if you use a French pronunciation. And Skamokawa is pronounced "Ska - MOCK - ah - way". Just remember that many of the place names are Chinook and Nootkan with second-syllable stress.
It will be a great trip with near-perfect weather that time of year - - enjoy!
Best - J
PS - I'd recommend US 101 south from Port Townsend down the west side of Puget Sound rather than Bremerton - which is still very densely populated with high traffic.