AFAIK if you are "permanently" bringing a car into the US, or bringing it in with the intent to sell or otherwise transfer ownership
to any US party, which would include a junkyard or charity, you need to formally import
it. And that might require DOT and EPA compliance issues, tariff, all sorts of regulatory tangles.
But on the other hand, scrapyards do sometimes just "make it disappear" although they won't pay you for that.
So that's something you want to explore with the powers that be. There are plenty of Canadian snowbirds in Florida
, surely, someone would be willing to take it off your hands and bring it back to Canada
if that's the simplest solution.
You may also find that, needed or not, it makes your entry easier if the "cruising supplies" are all in closed boxes prominently labeled "Goods for yacht in transit" with the yacht name on it. Technically, no, you're not shipping
things to a yacht in transit out of her home waters, but wtf....the yacht will be in transit, you might just confuse a US land crossing border guard, and when they're embarrassed at unfamiliar things, sometimes they just wave you on to get rid of you.
Too much alcohol, tobacco...Yeah, there are probably some limits on even THOSE kind of supplies.(G)