Did anyone ever put a P-51 on floats? I suppose it's possible, given that it's a model.
It appears to have a single cylinder nitro engine sticking up from the cowling, which suggests that it's RC.
I don't have a specific make/model in mind, but it looks to me like it could be a Schneider Trophy racer. Perhaps that's a number "1" or "7" on the aft fuselage, and maybe a sponsor logo on the wing?