Other than recommendations people dont have much more to go on! Remember that floatplane flying is pretty rare in the UK and possibly Europe too, not many places to go. I take it your from canada and that it's a different game over there, and as such you will know the pit falls and which instructors/schools to go to. For what it's worth my instructor had several thousands of hours and was a retired twin otter floatplane air taxi Pilot, I reckoned that he knew more than me!
For most people it will only be for a one off lesson, another experience for the logbook and not something that they will undertake on a regular basis.