Definitely have blueberries, although they are just going out of season. Still, you will probably get lucky.
If you have time right when you enter Maine, let me know! I live right at the Southern tip, in South Berwick, which is by York and Kittery.
If you are coming up through NH, stop at Jenness Beach in Rye, or Odiorne Point (beautiful) and also stroll through Portsmouth NH (have coffee or lunch at an outside table at Popovers, and Cosmo Edward can sit right with you. (Portsmouth is a very dog-friendly town.)
Kittery outlets: If you want to shop you can stop here. The best outlet is probably JCrew, but the most popular store is the Kittery Trading Post which sells everything from guns and tents to flannel pajamas and running shorts. Like a local LL Bean.
York: Stop at Stonewall Kitchen, right off I-95. Excellent local (but sold nationally) store for jams, marinades, sweets, cooking utensils, with an attached cafe. Tastings throughout the store. Worth a stop.
Ogunquit or Perkins Cove: Continue from Stonewall Kitchen right up Route One. I agree with Diana: park and walk the Marginal Way, a super gorgeous walk right along the ocean. The path is bascically carved into the rocks that line the coast. Perfect for Cosmo Edward.
Portland: Get back on I-95 and drive to Portand. There are fantastic restaurants (I can give you some suggestions if you have special requests), great walking along the water so another nice place to stop with Cosmo Edward, cute shops (I can give you more detail here) -- let me know.
Freeport: A little farther along from Portland, definitely stop at LL Bean (open 24 hours). Freeport is a whole outlet town, so you can go crazy (Northface, Cole Haan, etc.) but LL Bean is the place to go.
I hope this is helpful, Karen!!! Please message me for more, and I would love to see you if that works out!
Vivian