The Faculty of Graduate Studies provides information about housing on campus (Keele & Glendon) with basic, but useful information and links to off-campus housing:

The following link brings you directly to housing options on the Keele campus:

Places4Students is a site which tailors apartment and roommate listings to areas close to university and college campuses in North America:
York University page
University of Toronto (downtown) page

In December 2017, the Line 1 extension will open with two stops on York University’s campus, “York U” and “Pioneer Village,” reducing travel times significantly from Toronto’s many neighbourhoods south of campus. Nothing replaces strolling through the different neighbourhoods to get a feel as well as to call numbers on “for rent” signs.

Online sites, such as Craigslist, Kijiji, PadMapper, and ViewIt list various rentals and at least can provide one sense of types of availabilities and rentals amounts:
Craigslist housing
Kijiji real estate (use list on left side: “room rental, roommates” & “apartments, condos”

Some students have also had success with different Facebook groups, which one must first join, such as:
Toronto Prospective Renters
Homes for Queers Toronto
Bunz Home Zone

Additionally, always check the Toronto Bedbug Registry