Would it be possible to obtain the number of residential address (or total number of houses) at the zip/postal code level (three digit level) for Toronto, Canada? Where might I find such information.
I believe you can purchase it from Teranet but this kind of information is extremely expensive and possibly confidential in Ontario.
Alternatively, you could download free data from Land Information Ontario (LIO). GTA has a 1:10000 coverage and a few buildings datasets, large buildings (polygon footprints) and building locations (centroid points). This data does not include adresses nor does it contain very much detail such as building types, etc. You may be able to assign addresses to the buildings if you download roads from Natural Resources Canada - this is a regularly updated Federal road network and I believe the segments include address information.
I am not in Toronto so I don't know what you can get from the city planning division in terms of data. In other Canadian cities detailed geospatial information including pins and parcels can often be purchased.