When a city has more than one airport, not only the airports have designators, but the city as well. Two more that you can add to your list are YEA (Edmonton) with YEG and YXD. Then there is YMQ (Montreal) with YUL and YMX.

Why your bags would have been tagged YTO is a mystery. If flying into Pearson, they definitely should show YYZ.

BTW, a lot of international cities also have a city designator as well as an airport. You can include PAR (Paris), TYO (Tokyo) and MOW (Moscow).