You will be good to go with high performance seaplane, even if you use the 172. FAR 61.31(f) says "...….to act as pilot in command of a high-performance airplane (an airplane with an engine of more than 200hp)….."
This is a one-time logbook endorsement, not a rating on your pilot certificate, and is good for all high-performance airplanes, no matter what class (single, multi, land, sea).