Zeeter I fish the US side at least 2 days a week for the early season smallies , 2 years ago I was in the Buffalo harbour area and seen a US coast gaurd boat floating around so I pulled up to ask them that very question. The answer I got was that if your launching from the Canadian side and returning the same day then all you need is what is required by the Canadian coast gaurd . If however your are towing your boat across the border and launching from the US side you will require the US safety equipment. If you are travelling for an extended stay and launched from the Canadian you will need the US safety equipment.
Also I always bring my passport just incase of a unforeseen problem that forces me to land on US soil or if I'm forced to anchor. I also have the US border patrol phone # loaded on my phone to make the call in an emergency situation.
I hope this helps just remember this is 2 year old info so take it for what its worth. I follow these guidelines and have never had a problem.