The question is specifically how to avoid US airspace. There are plenty of direct flights from Latin America to Canada but they all pass through US terrestrial or oceanic airspace.

So you can stop at Havana or Varadero, but then you’ll still be passing over the Florida, North Carolina and New England coasts controlled by US-towers, on your way to Canada. It’s so far an unfounded fear but I’m entertaining it just to see the circuitous route you’d need to take to avoid it.