There are two things you need to know for the MCAT. The first is you need to know your basic science course material...biology, chemistry, physics...along with how to write. The second is you need to know how to take a standardized test...how to pick up on the tricks the test writers throw in.
If you're really worried about taking the exam, take a prep course. I don't know what's offered in Canada. In the US, there are test prep companies like Kaplan and Princeton Review that, while pricey, do a good job of preparing you for these exams. They will administer a lot of practice exams, give you study guides, and help you sort through the tips and tricks. I don't know of anyone who doesn't take one of these courses, or something similar, to prepare for the exam...or at least get the study guides from someone who has taken the courses.
In the US, there are different exams for medical school vs. veterinary school. So, that's also something to be aware of, in case medical school isn't your plan and you're thinking veterinary school.