There are some eloquent arguments here as to why you shouldn't prepare for admission tests...

http://interpreting.info/questions/3279/any-advice-for-preparation-of-entry-examination-to-sino-european-senior-interpreter-training-program-hosted-by-uibe-china

The gist being that these tests are meant to test your aptitude, not your ability. (Will you be able to interpret, not can you interpret).

If you had to pick two useful skills at an admission tests then being able to speak well to an audience (in spite of your nerves). That would mean both how you speak, but also being able to think on your feet and say make sure what you say is intelligent/appropriate. Being able to summarise information is also very useful. Can you listen to a short speech or presentation and summarise it (which assumes that you recognise the important and less important elements of it and recall the important bits) - including the logical links within the speech.

It's difficult and may even be counterproductive to try to practice these skills without supervision from conference interpreters.

If it's U of O you have your heart set on, start by writing to the Chair of the School of Translation and Interpretation to find out the latest format of the exam. In the past, the exam has included components on simo with text, public speaking, and current events.

There is also a program at Glendon College, York University. For more on the Glendon MCI, have a look here: http://www.glendon.yorku.ca/interpretation/