Viewit.ca, craigslist.org, housingmaps.com, mls.ca, myhood.ca
Tell him to pick up the Renter's Guide books that they have around the city, next to the newspaper stands. It can give you links to property management websites and you can see their listings directly.
If he doesn't hate the idea, think basement apartments if he wants the cheapest possible housing option. I've not had the best experience with basement apartments, but for a student, it might not be a terrible option.
Tell him to walk around any neighborhoods he think he may want to live in. There are usually a bunch of for rent signs, or large wooden signs outside of apartment buildings. He can go to their website, or call right in front of the building and ask to see a unit.
Personally, I wouldn't want to live around York campus (I'd take the commute from downtown, thanks
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).