101 around Olympic National Park is OK. There will be some traffic, including trucks, but you will need to get used to that anyway going down the coast. There are not a ton of services, but enough to keep you going. You can look on Crazyguyonabike.com and find many, many journals of cyclists who have taken this route.
As long as you are flexible on your schedule, you should also consider making the San Juan Islands (off the coast of Anacortes, Washington, between the US and Canada) as part of your trip. You can ferry there from Anacortes or from Seattle. You could spend a day on San Juan Islands, Orcas Island and Lopez Island, or just two of the 3, and have a great time. Easy enough to schedule either on your way to or from Vancouver.