The only major difference is with regard to "Lateral Marks", buoys marking the safe limits of navigation channels. Us europeans have the red ones on the left on the way in, whereas the yanks have the red ones on the left on the way out.
I can't imagine floatplanes have a great enough draught for that to matter much (more a question of not bumping into the darned things).
The rules of the road (rules for the prevention of collisions at sea) are standard internationally, and have specific applicibility to seaplanes when manoeuvring on the water (rule 3 "the term vessel means any form of water craft, including non-displacement craft and seaplanes, used for or capable of being used for transportation on water" if my memory serves me correctly).
