I don't think there can be any secret spots in the GTA anymore...When I was a young lad living in the east end (TO) we used the TTC to get to the Grenadier Pond in High Park or to the ferry boats to the Islands or Humber Bay, Etobicoke creek or the Credit River...There is also the Leslie Street Spit or Ashbridges Bay for carp...Eastwards there was Highland Creek, Rouge River and Frenchman's Bay (both open water and ice fishing at Frenchman's)
I have to add that I haven't been a young lad for many years (70) and lots have changed since when I last fished there...Best of luck !