@ Abhay What I could gather from reading in different forums is that in Canada there are three kinds of driving license(s) the G1 G2 and G I might have got the naming convention wrong, but the difference is that one is absolute basic learner's license the next one you can drive with some restrictions like can't go on the some highways and freeways and other such restrictions, The G license is the full fledged license.
Now I am assuming that you have been driving in India for more than 2 yrs, or lets say you have held a valid DL in India for more than 24 months, then what you should do is get a letter/certificate of authenticity from the DL issuing office in your area, from where you had your license made. It is a very simple letter just telling your DL number and for how long you have held it.
Now when you land in Toronto, you need to take your DL, your Letter of Authenticity and go the the License issuing office in Canada write an exam and pass a practical test and Vola !!! you have the G license straightway.
Now the catch is, you should practice a lot for the left hand drive there, plus the book from which you need to prepare for the DL exam is available on the net, just search for it and you should get it. Better prepare from India itself.
Also Indian D/L is valid for the first 6 months when you land there.