You can most definitely use miles for an award ticket to Cuba, as long as they are not from a US FFP. I was able to find business class award availability on NYC-PTY-HAV (a through ticket that cannot be bought for money) on COPA. The funny thing is that COPA frequent flyers aren't able to buy award tickets to HAV, as their "home" FFP is that of Continental!
Having said that, I wouldn't buy that ticket if I were a US citizen...It's just asking for trouble. Go from Canada on AC miles or something.