Several tour companies offer trips in Washington's San Juan Islands. Low traffic, low to moderate mileage. A couple of big climbs (like Mt. Constitution) are typically optional.

Here's the link to the one by Backroads:

http://www.backroads.com/trips/BPSI/...ds-biking-tour

Another similar outfit is Bicycle Adventures.

Here are there San Juan Island tour options (they have many others):
http://www.bicycleadventures.com/where/washington/