Even though it after the original poster's tour time, thought I weight in here since I just returned from touring Cape Cod. We started in Mattapoisett, MA and rode ~25 miles to Shawme-Crowell state park in Sandwich. Picked up the canal road in Bourne & rode over the Sagamore Bridge.

From Shawme, we rode to Wellfleet, with a side trip to Nauset Beach, We had a little bit of a messy time in Hyannis, winding up down there trying to maximize bike path time. We used the service road aside of route 6, Picked up the Cape Cod Rail Trail (CCRT) and took that to all the way to Wellfleet (w side trip to Nauset). We had a little bit of a messy time in Hyannis, winding up down there trying to maximize bike path time.

Wellfleet back, we stayed on the CCRT, but decided to stay North. That put us on Route 6A for a while which even though the section we were on is listed as a bike route, has no shoulder and lots of traffic. We took 132 south and worked our way to Service Road on the way back - over Sagamore, Canal road back to Mattapoisett for a 65-67 miles day.

Touring the Cape is generally going to be like this I believe. There's the smooth great rail trail, when off it, or other bike paths, if you are trying to get somewhere, you will likely wind up on a busy road with little shoulder.