Ospreys are often seen in storm water ponds around GTA - these ponds are full of goldfish and catfish. One close to home is Milliken Pond in Scarborough, I have seen them getting fish in Downsview Park pond. Mill Pond in Richmond Hill also gets an Osprey or two. I used to go to a pond in Richmond Hill near Bayview and MajorMac beside the Walmart for Ospreys as they visited the pond quite regularly from mid July to mid Sept. The pond supported a wide variety of wildlife. Besides Ospreys I have seen Minks, Green Herons, Blue Herons, Black-crowned night herons, Kingfishers, Cooper's Hawks, Cedar Waxwings, Kingbirds, and many more around that pond. Two years ago the town drained the pond and dredged it. Since then very much all fish loving wildlife disappeared. The Oakbank Pond near where I live faced the same fate in 2014. The other place to see Ospreys fishing is in Valley Inn, Burlington. Last year I spent good amount of time there in August. Good thing about Valley Inn is that you also get to see Bald Eagle, Great Egrets, Terns and many more. I have taken photos of Ospreys fishing in Grand River near Belwood Lake area and also in Brantford. They are everywhere, even in Hight Park. Yes, I have taken photos of them diving in Grenadier Pond. Reesor Pond and Toogood Pond in Markham are also two ponds that saw Ospreys visiting for fish.
Carden is a great place to go in the beginning of July - you will still see a variety of grassland birds, warblers, Sedge Wren, Loggerhead Shrike (if you are lucky), American Bittern, and may even see a Bear or two. It is about hour and half from Toronto. Late July or early August some of the Sewage lagoons (e.g. Nonquon) could be a good option to see returning shorebirds, Black Terns, Warblers, and many more. Presqui'le is another great to see shore birds in August, Sept. In Sept you can cross over to Gull Island to see some more shorebirds. If you haven't already, you should subscribe to eBird, check out OFO website for their hotspot locations etc. There's a book out about Ontario birding hotspots - check that out.