@Sam2019 Last time i was in cuba foreigners could buy sim cards but it was quite expensive and the lines were longish, if you have a cuban friend however they could probably help you out or if you are staying at an bed and breakfast ask the owner they might have some ideas/options for you.
@Sam2019 your phone service will NOT work in Cuba. PM does not provide roaming service there (PM only has roaming in USA)
if you need data service, get local data prepaid service . Also signup a VoIP app like TextNow. TextNow will assign you another number so you can make free calls and text back to Canada, . With the app, you can also receive calls and text. TextNow will work as long as you have Wifi or Mobile Data anywhere in the world