Review their website
Get prepare with good concrete example of your ability of work
They may ask you about your previous accomplishments and you should be very well prepared for that.
I was not interviewed for uOttawa, I was brought on as a result of enthusiasm in the course I took previously. I was asked to come back by one of the teaching assistants from that year.
Within the CITE, my interview process was informal, and focused on assessing whether I could use my technical knowledge to minimize disruptions as quickly as possible for clients. You should be comfortable working with soundboards, and your attitude should be relaxed but solutions-oriented, since the clients themselves are likely to be stressed (at you/us) if something goes wrong.