You are in Canada as I remember, so this may not apply.
Check out a school like you would any other outfit.
What is their reputation? Are the costs normal? Are they fully accredited by whoever accredits schools in Canada? Are any credit hours transferable to another school? What is their record for job placement? Most technical schools maintain close contact with large area employers. If you have our equivalent of high school guidance councilors, what do they know about this school?
Ask for references from former students and employers who have hired graduates. Is their equipment up-to-date and well maintained? What are the qualifications and work experiences of the instructors?
Google would probably be where I would start, if there is something negative about the school, it should show up in comments, old news stories, etc.
Edit:
By all means, take a tour! Ask if you can sit in on a couple of class sessions, that shouldn't be a problem. At most, they might ask you to sign a liability waiver. If they say "we don't do that", I would be very skeptical. That's the best way to see if you think it is a fit for you or not.