From a Canadian friend who has been there a few times:
The answer is not related to beaches South of Cuba but an Island South of Cuba.
The Island is called Cayo Largo. You can fly directly to this island from charters departing Montreal or Toronto. The island has little to offer except for beaches...no village to visit, no shopping, no golf etc. There are about 4-5 resorts: the Sol Cayo Largo, the Pelicano Cayo Largo being the most popular. The Pelicano harbours many folks who do not know about the nudity until they walk the beach with grandma and the kids.
The beaches in front of the resorts are mostly for textile bathing but off to the side, nudity is the preferred mode of undress. In fact, you can easily walk 6-7 kilometres in the nude...right up to Paraiso beach.
The resorts are 3 stars at best with 2 star food.