Unfortunately, the website for the Toronto bus terminal at Dundas and Bay is not working. I have called their main number (416) 594-1010 and left a message enquiring about storage lockers for luggage and their sizes. I will post the information here if/when they return my call.
There are definitely no storage facilities for luggage near the ACC except for hotels that will keep a customer's bag for a few hours once they check out. You may have to leave your luggage at your hotel, then return there to retrieve it, before going to the bus station, if there are no other options that come up.
Edited: 6 years ago