We have three launches for different wind directions in the city, and the only one at this time of year which has the space you need as a beginner is Hanlan's Point on the west end of the Toronto Islands.
Check out the Ontario Kiteboard Association page for it and other launches. localkitespots.com also has some good information.
Cherry beach is simply not a suitable launch until you can ride upwind and have your self-rescue procedures nailed. The kite launching and landing area is very small and turbulent due to the nearby trees, and the 'beach' is actually quite rocky below the water line. I haven't been down there in over a month, but I was talking with a lifeguard at Hanlan's on Sunday, and he told me it's getting a bit crazy down there; too many kiters going through the swim area. Ashbridges is just too crowded in the summer; you have to be able to stay upwind without drifting into the swim area on the easterlies which are appropriate for that location.
None of the Toronto launches are ideal for learning, they're all open to the lake, get deep rather quickly and develop appreciable windswell in only a few hours. Hanlan's has the most space, but can get shorebreak which is downright intimidating when starting out; and for some reason, lots of guys seem to have trouble getting out past it--especially when the wind is directly onshore. The trick is to body-drag with your board out past the break, then go from there. Of course, they could all just be a pile of idiots who like riding 10 feet from the water's edge with their kites overflying the beach and zero room for error. I'm not sure if this is a problem of skills or education--maybe both.
You can filter spots for 'beginner' on localkitespots.com, that should help you find other launches--Please use them! OKA Matt Aiken has spent a lot of time and effort with various authorities securing the launches we do have, and we need to use them responsibly to preserve access. Setting-up outside the designated areas could create problems. The vast majority of guys you'll find at the beach are friendly and always willing to lend a hand. Don't worry about mixing-in, just ask the locals if there's a better area at the launch for you to do your thing; but really as Bob said, it's the responsibility of the more experienced guys to avoid beginners.
I *might* make it out to Hanlan's tonight (but probably not until next week). If you want, PM me, we can exchange contact info and I'll let you know the next time I'm headed to Hanlan's.
P.S. Even in the height of summer, Lake Ontario can get FRIGID. I was at Hanlan's both Saturday and Sunday on the gusty northerlies available there. Saturday, I could have gotten away with a shorty or no wetsuit at all. So when I went on Sunday I didn't bother bringing my steamer, and brought only the shorty instead. I immediately regretted the decision; the offshore wind had pulled a bunch of cold water from the bottom to the surface, and it was freezing. Check the attached image, it was 54 degrees Fahrenheit, maybe less. As a beginner, you'll be spending more time in the water, and when it's that cold it will sap your strength very quickly. You need a wetsuit if you don't have one already.