I wonder what the heck this means? I've noticed that Canada is really acronym-happy. Whereas in the US the same thing exists, it is limited pretty much to government weenies and the military.
In Canada it's different. Even third graders there probably know what GTA means.
Alas, I have no clue...
This includes the Town of Markham that abuts Toronto to the north.
Here's a few other Toronto-centric acronyms used daily: TTC, DVP, ETR, QEW, ACC, MLSE, GST, PST, TSX, TIFF, ROM, AGO...