Too bad the ferry from Yarmouth NS to Maine is no longer running, I would have suggested going along the south coast of Nova Scotia, which is probably the most picturesque coast in the Northeast. You can still do it and go around to Digby (or get there via the Annapolis Valley) and take the ferry to Saint John NB.
It has been a while since I've cycled the Fundy coast of New Brunswick, before they 4-laned NB1, so I don't exactly know what's happening there. Seems like the secondary highway routes have been segmented, and I don't know if they will let you use short sections of the freeway to get from one to the other (I don't see any "no bikes" signs at the on-ramps on Google street view)
I personally found cycling in Maine a bit uninteresting, you rarely get a view of the ocean because the highway is inland among the trees, but the roads have good shoulders.