Hi Carine,
I recently completed my MA in Art History at McGill and I absolutely loved it. Let me know if you have any questions about the program and faculty!
I think your choice will depend on many factors such as your area of specialization and whether you hope to pursue a career in academia or in the artworld. I considered both programs for my MA and ended up at McGill because I specifically wanted to work with certain professors and I wanted to write a thesis.
The programs are quite different. McGill's is a small 2 year program with thesis, UofT's is a larger 1 year program with no thesis.