Short version: The US is the 800-pound gorilla of North American trade. It can, in fact, have that huge an impact. To put it in perspective, Canada's a much bigger and better-equipped nation than Cuba - and we would be devastated economically if the US cut off trade.
I don't doubt the US could have a large impact economically, but I am saying that right now, if Cuba's economy is crappy, it's not the US's fault because Cuba has
access to the rest of the world. If the US had had Cuba under a naval blockade prohibiting any ships from coming or leaving, then yes the US would be responsible, but since we haven't and Cuba can trade with the rest of the world, Cuba's economy isn't our concern, and in the end, it is up to the Cuban government to what it allows inside the island nation. If they restrict what we could trade, that means its their fault for any remaining crappyness of the Cuban economy.
This. I'm not one to tout American exceptionalism (though on the whole we're pretty okay despite some public blunders) but we are a big trading partner, and we're like 90 miles from Cuba, proximity and bulk are the two big factors here.
A NOLA-Havana trade route would be pretty good for Cuba. Plus there's the Tourism bucks Cuba's been missing out on for the last half century.
*nods* Still, it's the Cuban government that is pulling the strings in this situation. I am just very distrustful of that government and of our own current administration and of the party that fawns all over communist dictator types.