There are plenty of places, although daytime parking can be problematic in many of them in the summer.
Outside of swimming hours, it's a bit better. In fall, you rarely get hassled.
Anyway, you're going to have to narrow down your choices a bit because whole books
could probably be written about Cape Cod Bay. For starters, I'd suggest Old Sandwich Harbor,
Barnstable Harbor (Bone Hill Rd, Scudder Lane, Indian Trail town landings), Brewster Flats
(Robbins Hill Rd, and Breakwater Beach landings), Sesuit jetties, Chapin Beach, and Pamet River in
Truro. Each place has its tidal idiosyncracies and some of the places I haven't fished
enough to know that well (like Pamet, for example).
Email me if you have specific questions about a specific place...
-bd