Here is a link to the Toronto Ornithological Society with a suggestion for hot spots for birding:
http://www.torontobirding.ca/hotspots.php And here's my personal list of my favourite places:
Leslie Spit (Tommy Thompson Park)
Don Valley park system (E.T. Seton, Taylor Creek, Charles Sauriol, etc)
Edwards Gardens (technically the same park system as above but since it has so much more than just a walking trail I put it on it''s own)
Bluffers Park
High Park
And lastly some advice from Norm Murr when I asked a similar question:
"Don't forget the Toronto Islands.
Best in April and May and then again from mid August to the end of October.
Many Warbler and Sparrow species as well as rarities such as LeConte's, Sharp-tailed, Lark, Grasshopper and Clay-colored Sparrows, Hooded, Worm-eating and Kentucky Warblers, Yellow-breasted Chat, Western and Summer Tanager, Sedge and Marsh Wrens, Black-backed Woodpecker, Harlequin Duck, Eared Grebe, Yellow Rail, Chestnut-collared Longspur, Tufted Titmouse, Yellow-headed Blackbird, Variegated Flycatcher, etc. All of these have been seen in the last 10 years down there."
If you need any advice on getting around the city via transit feel free to ask. I am a transit operator and I know the city fairly well... at least I know how to get around it using transit... including getting around the transit construction during the summer lol.