I agree with the others to not take the ACA route through Washington. If the book you are planning on getting is "Bicycling the Pacific Coast" by Kirkendall and Spring they have two better routes - on either side of the Olympic Peninsula. Oregon puts out a pretty good pamphlet on cycling their coast which I used and found very useful. For California I used ACA Pacific Coast route maps. I think they were better than the book for that state.
As for starting in Vancouver it really depends on whether or not you come into the city. If you fly into the airport you will actually land in Richmond and can start heading south immediately. The most direct route will entail loading your bike on a bus to get through the George Massey tunnel.
If you decide to spend some time in Vancouver then I think you can't do better than Stanley Park as a starting point for your trip. If you have the time, a ride around the Park along the seawall would be a great way to start a tour of the west coast. Even if you decide not to do the full tour around the park the seawall bike path connects to routes to get you started south. There has been a great deal of work done in Vancouver over the last 4-5 years so it is now much easier and safer to get out of the downtown area. I doubt that either the book or ACA maps are fully updated on the newest routes in the city.
The following link shows most of the bike routes for the greater Vancouver area.http://www.translink.ca/en/Getting-Around/Cycling/Cycling-Maps.aspx
This link gets you info on cycling in Oregon. Use the link to order a hard copy of the Oregon Coast Bike Route.http://www.oregon.gov/ODOT/HWY/BIKEPED/Pages/maps.aspx#ODOT_Maps