This is our experience as us citizens who flew from YYZ to SXM and return june 2017 and June 2016.
To SXM. Your bags will be prechecked by us customs in toronto to SXM.
Return from SXM to YYZ vis U.S. . Our bags were checked all the way through to YYZ. We did not claim them in either Charlotte or Miami the last two summers.
You and your carry ons go through immigaration customs and security to cathch your connecting flight.
