Consider taking the ferry from Port Angeles to Victoria, then drive up Vancouver Island to Comox. From Comox, take the ferry over to Powell River on the Sunshine Coast and make your way down to the Langdale ferry near Gibsons which will take you to Horseshoe Bay in West Vancouver. From Horseshoe Bay you have the option of: 1) going back to Van. Island; 2) heading northward to Whistler and on to Pemberton; 3) heading eastward to Hwy no. 1; 4) heading southward back to the Canada/US border. If you drive the Island and Sunshine Coast loop, you will see some of the most wonderful sights and scenery that the southwest coastal area of BC has to offer.
Victoria, (BC's capital) is a very interesting and unique city. LOTS of old well-preserved houses and buildings. They say it's "more English than the English". If you have the time, there are many great things to see like Butchart Gardens, Craigdarroch castle and the Empress Hotel. High tea at the Empress, the Blethering Place tearoom in Oak bay and James Bay Tearoom are all fun to visit if into that sort of thing.
If you don't have time for the San Juan Islands (very beautiful), consider taking the Wa. State ferry from Whidbey Island over to Port Townsend. From Seatac you could drive down to Olympia and head up hwy 101 on the west side of Puget Sound up to Port Townsend or Port Angeles.
What about flying into the Bellingham airport near the border? It's a LOT less congested than Seatac and you will avoid the Seattle area traffic which can be pretty bad. You could also fly back out of Bellingham. The Vancouver airport is another one to avoid if you can (busy and expensive due to airport fees). Many Canadians drive down to Bellingham airport as flights cost a lot less from there.
