If you are going to Tampa and then out to Canaveral, you should look into buying a package offered by Busch and Sea World, you can buy passes that allow you to do both parks. I think Universal Studios is included as well. If you are a roller coaster family, Busch is a great park and then Universal Islands of Adventure.
As for the rental, just call the agency and ask them if they allow this or if there is a fee for dropping off in a different location from where it was picked up. I am sure you can do this, there may just be a fee attached.
Enjoy your trip.