Jorgelito has some good advice--don't rely on the bookstore for textbooks. I used to order all of mine off of Amazon.com. I could order used texts from a number of different sellers at once, and got a number of really good deals. But there are some instances where new books have to be bought, because it's a brand-new edition or whatever. In that case, compare the price from the bookstore with that at Amazon--sometimes one is cheaper over the other. Just tell your son to make sure he has all the information he needs to track them down, specifically the edition needed and the ISBN if possible.
And as Jorgelito suggested, many profs put the textbook on reserve at the library, or else it's part of the regular collection. It's worth figuring that out prior to term, as once term starts loads of other people are going to have the same genius idea, and if it's part of the regular collection, it will get checked out fast. Also, if it's on reserve, and your son plans on just using the reserved book, he should aim to get his work done for that class a day ahead of time instead of waiting till the last minute like everyone else will, otherwise the book will be checked out. If he plans on using a reserve text at any time, he should also figure out how to access the online card catalog from home:
Ryerson Library Catalogue because it's totally disappointing to show up at the library planning to use a text on reserve only to find out some jackass checked it out. And photocopies are good! I don't know about copyright law in Canada, but here in the United States photocopying texts for educational purposes is fair use. For many of my classes, I found photocopies easier to use than the full textbook.
Oh! And don't buy textbooks until after the start of term!!! Especially in classes where there are multiple sections with different instructors, your son may end up not even needing one of the books listed. He should have all his syllabi in hand prior to purchasing books to see what he really needs to buy. It may be that he only needs to read 10 pages out of book B for class C, and he can borrow a classmate's copy to photocopy, or it's on reserve.