by far the best aerobatic seaplane is the ARF Ace Seamaster - it does the easiest and best slow and point rolls of any seaplane - and most land planes.
this is despite the pylon mounted engine -a 70 4 stroke works out just about best.
We have had more than 30 of these at our lake and they all fly great - anything from a 50 2 stroke to a 72 4 stroke works well-but the 70/72 power is best for aero.
rolling circles,16 pt. rolls, top hats,etc.-all are easy to do - and it lands as easy-
the only slightly demanding operation is on take off- apply power gradually and be sure the wings are level before adding power as digging in a tip float will cause a "ground" loop--as is true of all tip floats