One of the doctors at the office I work at was telling me that Waterloo tends to segregate different components of an application and rank each component separately.
So for example, components can be GPA, OAT, Shadowing Hours, LOR, Experience, etc. Each component is given a ranking, ie: A-C and some are weighted differently. GPA is quite heavily weighted and so is OAT. You did very well at your OAT so that should work in your favour. Then all the components are added up and they access the applicant based on that score.
Beware, the doctor I know has been practicing for over 10 years now so the admissions process may be different now with the improvement of technology to make shifting through applications easier.
I would apply for both Waterloo and the US at the same time. US you shouldn't have too much difficulty obtaining an acceptance. I'm not sure about Waterloo though. From personal experience, Waterloo is very competitive since it is the only English school in Canada and receives a lot of competitive and qualified applicants every year. They also base the 'early filters' of weeding out applicants on academic portion of the application. Assuming you get through the threshold for academics, your shadowing, volunteering, etc need to help push you through the rest. I also know another optometrist who recently graduated from Waterloo, he was initially put on Waterloo's waitlist and was planning to go to the states, but last minute got taken off the waitlist. I know this isn't a lot of information, but I hope it helped.
Good luck!
Scholarship Access: Becoming a Student Doctor course
