Toronto. Most ethnically diverse city in the world. You can obviously tell frmo this, that there would be tons to do.
The places I usually take visitors for a visit to Toronto or the great toronto area is usually as follows.
Downtown:
CN Tower - Visit to Toronto isn't complete without this. Tallest free-standing structure in the world, and has the highest observation deck in the world. You can literally see New York state from the CN-tower. This is also known as the symbol of Toronto itself.
Sky-Dome & Air Canada Centre - Home of Toronto Blue-Jays, and Toronto Raptors respectively.. Home of Vince Carter :)
Yorkville - Downtown toronto's nightlife district.. If you have time, check out Berlin.. that's one of my personal favs.
Lakeshore Blvd/Meow Nightclub - Lakeshore Blvd, good for just scenery, and has anothr one of my fav clubs, Meow, situated right in front of the West Harbour.
Queens Park/City Hall. Great if you want to see some good Canadian riots.. :)
ROM - Royal Ontario Museum. If you're into the wh ole museum thing, alot of artifacts on Sikh culture, and other religions as well.
Ontario Place - Great for the beach, harbour, and the IMAX theatre.
University of Toronto - Canada's most prestigious university. Birthplace of Pennecilin, and many other discoveries.
In the Greater Toronto Area:
This would all depend on your ethnic background. But, we have our own Little Italy (St Claire Ave), Little India (Gerrard St (downtown), Malton, NE Scarborough), Little Greece (The Danforth), Little Persia (Warden & Laurence) in Toronto, as well as variety of other places. Great place to see the true ethnic diversity of the city :)
Tons of movie theatres. Countless number of them, and some theatres dedicated to showing Indian films, Persian films etc. and tons of restaurants! Including mine be sure to visit Boca Osteria Ristorante in Brampton, located on Queen Street West, and George, downtown Brampton.
For shopping. I recommend
Eaton Centre - Largest Downtown shopping centre in North America.
Downtown itself - Lots of high-street shops
Square One - Located in Missisauga, excellent clothing shops, designer wear is readily available.
Yorkdale - Located in North York, another great place. Similar to Square One.
For the Studious:
Ontario Science Centre. - This place is simply AMAZING. Great for science buffs.
Places outside of the GTA, but close enough to VISIT and a MUST SEE.
Niagra Falls - One of the 8 wonders of the world. The largest waterfall in the world, and also known as the Honeymoon capital of North America. It is a great place to see during new years, when Canada and the US have a good competition on fireworks displays.
Also, if you have your visa, passport on you while you're at Niagra falls. You can also take a quick trip to the United States, since it's just right across the bridge.
There is many more things that I may have forgot to mention, and I will leave this to my fellow ontarians to fill.
Arai