I’m mistaken. The best I could find in support of my claim was this in Wikipedia:

The Helms-Burton Act has been the target of criticism from Canadian and European governments in particular, who object to what they say is the extraterritorial pretensions of a piece of legislation aimed at punishing non-U.S. corporations and non-U.S. investors who have economic interests in Cuba. In the House of Commons of Canada, Helms-Burton was mocked by the introduction of the Godfrey-Milliken Bill, which called for the return of property of United Empire Loyalists seized by the American government as a result of the American Revolution (the bill never became law).

I don’t know the exact mechanism but I believe our sanctions cause more than just a pain for American companies doing business with Cuba.