I agree with tacomee. I did the west coast from Victoria, BC to Crescent City CA last summer and the Oregon coast was for sure the best part. Consider doing it one-way with alternate transport back (we rented a car one-way). It took us just over two weeks but my brother was pulling a child trailer with a four-year-old and I had my 13 year old son on the back of a tandem. Shaving a day or two off the time should be fairly easy.
A nice loop into Canada would take the Anacortes ferry to Victoria, up Vancouver Island to Courtenay then down the mainland (search Sunshine Coast for route info) to Vancouver. I've done the loop twice and aside from some climbing it's pretty nice. Can be fairly easily done in 5 or 6 days. If you decide to do it PM me and I'll give you some tips on the Vancouver Island part. Lengthen the trip by spending some extra time in either the San Juan Islands (as tacomee suggests) or the Canadian Gulf Islands. There is also some nice cycling in and around Vancouver. Search for the Vancouver part of the Transcanada Trail. Vancouver to Hope and back could be done in 4 or 5 days without too much problem - do it as loop with a different route back.
If I had to pick though, I'd say Oregon.