The interview is more of a chat than an interview, its rather laid back. Most of the questions they ask are pretty run of the mill. You should be able to talk precisely about why is it that you want to get an MBA, why at this particular school and what will you do after you have it. You should be able to describe what it is that you do in your current job. The interviewer also asked me what kind of things I do for fun and what I think are my two greatest achievements. She told me she was born in the same city as I, so we had something in common to chit chat about.
Be prepared to ask them a few questions after they are done asking you. If you are an international student, this is the best chance you'll get at interacting with a Rotman person. Just avoid being negative. I asked her that though everything else seemed great about Rotman, I got the sense that the alumni network and career services weren't as great as Ivey or Schulich or McGill. Big mistake. She got all defensive and it got uncomfortable for a moment there.
Unlike a lot of other b-schools which have faculty or 2nd year students interview you, its a staff member (they have a bunch of people called Assistant Directors) who'll do it at Rotman. So it all seems like an exercise to gauge your spoken English skills. Think of it as an HR interview for a job.