Early October this year I did a trip to Victoria via the western route (Oregon side of columbia to ferry to Cathlamet) 101 all the way to Port Angeles (last time I did a more a waterly route coast including Gray's harbor)
Can you do 100+ miles a day? If so this will get you to Port Agneles in 3 1/2 day in time for the afternoon ferry crossings (there are more in the summer than Fall I believe) to Victoria.
From Victoria there are great bike paths to get the ferrys to the gulf Island or back to San Juan Island and Anacortes fi that is your pleasure.
I carried sleeping bag and tent and camped out the first 3 nights. I stayed in a pretty nifty youth hostel right in the hear of downtown victoria to get showered and 'ciitifed.'
You could do this trip staying indoors but there are a couple of places where the pickings are slim.
I had only 8 days so I opted to take the train back from Seattle. but it was a very good trip, and I would do it again. (well maybe try a more direct route to Seattle and go the opposite way to go north.
One of the highlights of the states side trip is the ferry across the Columbia. And if you could manage it stay at the old lodge on Crescent Lake (that is only about 30 miles from Port angeles; and mostly down hill! Beautiful ride along the lake.
I would be happy to tell you more but I encourage you to do this. And visiting in Victoria and biking on the islands is sweet. But they are hilly! There is a beautiful park on the water on Saltspring Island which I would recommend if you are into camping. Also lots of B&B's - some quite pricy. Lots of good information on the Candian gulf island on the web.
reply if you want more information.