I haven't found out why the Tuesday flight was cancelled yet, but there was a special WestJet flight (WS8984) that left YYZ this morning at 5 am and a special return flight (WS4278) that departed SXM at noon today. This is in addition to the normal flight (WS2276 and WS2277) that is scheduled to arrive and leave later this afternoon. I assume the additional flight was to take home those passengers that were scheduled to leave on Tuesday.