Hey Albert,
There are no PADI instructors in Cuba. I know AquaSub Scuba does PADI open water pool and class in Richmond Hill then travels with the class to do the open water portion in Cuba. This is not a referral letter. Your instructor actually travels to Cuba with you.
I think you might be able to get ACUC certified in Cuba but I don't know how they'd handle things. Also, the quality of your training is less about the agency and more about the instructor. I know all the instructors at AquaSub and I'd trust them to train me well. Hard to find out about instructors in Cuba.
AquaSub is also a TICO Travel Agency. So they arrange the vacation package to Cuba as well. Check out the trip section at http://www.aquasubscuab.com.
Doh, just noticed I misspelt AquaSub Scuba. <-= This is the correct link.