I have listed few places to visit...please add to this list if you know more!

1. 30,000 islands - 226 km
http://www.island-queen.com/index.php

2. Scenic Caves/ Suspension bridge & Wasaga beach -150 km
http://www.sceniccaves.com/green/suspension-bridge.htm

3. http://www.algonquinpark.on.ca/ - 250km

4. canada's wonderland -33km
http://www3.paramountparks.com/canadaswonderland/#actions

5. Niagara falls - 145km

6.1000 islands (gananoque & kingston) - 275 km
http://www.ganboatline.com/

7. Welland canal -131km
http://www.stcatharineslock3museum.ca/

8. African Lion Safari -100km
http://www.lionsafari.com/home.html

I will add Bruce Peninsula - Tobermory & Area (around Owen Sound).
If you like water - there is nothing better than this around GTA (If there is - correct me, I would love to visit there).

http://www.thebrucepeninsula.com/

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Mumbai Maazi Ladki ...