Although there are some common questions, they do vary. Don't try to prepare too much for the interview questions, it's not like a school exam. Just relax and answer all questions truthfully and completely. Search for "interview" on this forum, where some people have written up detailed narratives of their interviews, including what questions they were asked. I was expecting to be asked "Why do you want to live in the US?" but that didn't come up like it did for many others. I was asked how long I had lived in Canada, which completely surprised me. I couldn't see the point of that but that's the way it goes. Good luck.