There a Great Planes PT-20 that is a .20 trainer. If you wanted you could put it on floats, I would run a bit of a bigger motor in it if that is what you want to do. You could also get a Sig MK II that is a .20 Trainer as well.

Are you looking for an ARF or for a kit?

You also have to remember that floats will only work if you land the plane properly on the water (I have never flown with floats), they will not help you much if you nose it in.