Toronto will be your port of entry into Canada. You will have to clear customs/immigration in YYZ and collect all checked luggage. I have never tried getting between 2 terminals, but I remember seeing bus service that should be able to take you to T2. Assuming that you received all boarding passes in GLA, you won't be required to receive new boarding passes for your flight to YFC.

If you want to go shopping, then consider Square One in Mississauga. It's suppose to be one of the biggest(or busiest) malls in Canada. It should only take you about 30 minutes to get there from YYZ.

Dowtown Toronto is too far away like everyone has previously mentioned. The traffic can be quite notorious, which would mean that you would have chances of missing your connecting flight.

You can always wander around YYZ for hours.. Perhaps you want to look at all the construction going on at T-New? Watch planes?? I don't know what there is to do in airports, besides using the MLL.