registration of US purchase by Canadian
Where do you intend to "keep" or "cruise" the boat.
If the boat stays in Florida, you will have to pay FL. tax, and can register it there. This will NOT preclude you from cruising the Bahamas etc. Many vessels have a "flag of convenience", which has nothing to do with owner''s nationality.
As previously noted, the more expensive the boat, the more motivation to reduce or avoid sales taxes.
If you intend to bring the boat back to Canada, you can avoid the U.S. State taxes, and pay the HIGHER Canadian Provincial/GST taxes, and register it in Canada. I think (?) you have up to 30 days to get the boat out of U.S. waters (to avoid tax).
Going the other way, I "imported" my Canadian boat into the U.S. for a very modest fee. She was still "Registered" in Canada, but was legal to sell in U.S. (purchaser must register & pay State tax).