Seaplane hit the nail on the head. A Kadet Senior is probably the ultimate high-wing floatplane. When I was in the Florida Float Flyers in Tampa, there were at least six of them flying...with anything from a .45 2-stroke to a .91 4-stroke. ALL were modified with ailerons, and at least one was an ARF.

I flew a Senior Telemaster with an OS.91, 45" foam-core floats. It would take off in 8 feet, or at 1/4 throttle it made great scale-looking takeoffs.

Floats make trainers with flat-bottom airfoils MORE aerobatic.

All the other trainers mentioned will also work well. We tried a Midwest Aero-star .60 with Goldberg Floats for a club trainer. It came out to 12 pounds. We called it "The Uranium Trainer"-heavier than lead. I don't think it was the Aero-star, but I really try to avoid built-up plywood floats except possibly as baseball bats or to keep my car from rolling off the jack when changing tires. The Aero-star flew, and it was really sluggish at that weight. But it was really pretty, if that matters.

One last possibility would be the BTE Flyin' King. Much like a Kadet Senior, but with a semisymmetrical airfoil for better aerobatics and with flaps. Flaps can really help a seaplane because the steepen the glide and get your approach safely over the trees on the other shore of the pond.