Not a continuous bridge, but it seems like you can bike most of the Florida Keys, including a seven mile bridge. Although I notice that when I put the Keys route into Google, there's at least one section that says, "walk your bike the next 4 miles." I don't know if that means that biking is not allowed, or if Google just doesn't want to tell you to do it.
Cycling the Florida Keys Overseas Heritage Trail| VisitFlorida.com