Interview for Canadian visa isn't compulsory. Students will generally be called for an interview only if the immigration officers find any doubts in documents that students submit for visa. If called for an interview, be prepared to answer any question relating to your documents.

Some of the sample questions may be:
Why you want to study in Canada?
What are your sources of income?
Who will sponsor your studies?
Why don’t have good marks in your previous studies?
How can you assure you‘ll come back after studies?
Do you intend to work in Canada?
Why haven’t you got any recommendation letters?

These are the questions you may be asked. But be assured there is chance of not being asked any of these questions too. So review your documents and pick questions from it on your own and prepare for answer for those questions.