I just finished a Yorktown, VA to Seattle, WA tour. If you choose to go through Ellensburg and across at Snoqualmie Pass, the John Wayne Trail is most definitely the way to go! The tunnel under the pass is an awesome experience! Have lights though! After Bend you can jump on the freeway for about 7 miles and then connect with the I-90 trail system pretty much all the way into Seattle. Here is my route from Ellensburg to North Bend in two links:

http://ridewithgps.com/routes/1750133

http://ridewithgps.com/routes/805050

Except for the freeway section Ellensburg to Easton was be beautiful! The ride on the John Wayne trail is an easy one...the scenery is stunning the whole way to North Bend. It is also down hill for at least 30 miles from the west side of the pass.