I don't think that Open Skies changes much to that. AFAIK, AF can already fly from, eg, FDF or PTP to both US and South America. Open Skies has no impact on that. The only difference that Open Skies does is that other EU airlines could fly those routes too.
The economics of these routes, however, do not seem to add up.
What could conceivably make more sense is for LCCs such as FR or Easyjet to expand to US-Carribean routes with a hub in, eg, SXM or FDF.