While I cannot speak to any specifics of the MMI questions, I can give you some advice on how I prepared. The best way to overcome any anxiety about the MMI format (or really any problem you encounter) is to learn as much as you can. Google, wikipedia, learn how the format came about in Canadian medical schools. After doing that, the process seemed far less foreign to me.
This blog also helped...
http://mmiqd.wordpress.com/about/
It has a bunch of MMI-style questions covering personal, ethical and moral dilemmas. Since the traditional format for executing the MMI seems to be 2-3 minutes of reading the question/formulating a coherent response and 6-8 mins talking with a committee member, I would practice the daily MMI questions under these same conditions at home.
From what I've read, it looks like the emphasis isn't on exactly what you say, but rather it focuses on your ability to construct a logical response under pressure. As I mentioned above, I enjoyed the format much more than the traditional interview, despite being completely new to the style. The admissions staff is an absolutely wonderful group and dispelled any anxiety from the very beginning, so don't worry about that. Enjoy the beautiful new campus. Learn from the student tours. They sold me from the minute I arrived.
Good luck!
🙂