There is luggage storage available in all terminals at YYZ; it's run by The Travel Store. Thankfully they haven't closed this for "security reasons" - in the U.S. you can no longer store any luggage anywhere (except in the trunk of a car, or at a hotel if you can bribe them). What a pain!

See
http://www.gtaa.com/Index.aspx?Sid=N...ode2.7.3&Tpl=1
(scroll to the bottom).

In T1, The Travel Store is located on level 3 at the far right of the terminal behind the AC ticket desk, just before security for Canadian departures. Prices are a flat rate for 24 hours per item, and vary on the size of the bag. If I remember correctly, the maximum is $10 for one large suitcase.