From post 3 in this
thread. MM fails YUL-UVF
As per one world YUL - UVF appears to exist and has been confirmed by AA.
I could not find it a very quick check on
www.aa.com with a few random dates. Others hopefully can do a better search. Only seems to be as YUL-JFK-UVF or YUL-MIA-UVF. Poster may not being giving us all the information.
Edit: Now think MM is correct. Route given by poster was not correct imho
Edit 2: The thread linked in post 12 states YUL-UVF exists as single flight (seasonable)