This is what it says on their Graduate admissions process page (https://uwaterloo.ca/graduate-studies-postdoctoral-affairs/future-students/after-youve-applied/admission-review-process)
"Your application will first be reviewed by the academic unit to which you have applied (Department, School, or program). The academic unit will manage the supervisor review process, if applicable. Applicants selected by the academic unit are recommended for admission and the application is sent to the Faculty Associate Dean’s Office.
The Faculty Associate Dean’s Office then reviews your application. All applications approved for admission are then sent to Graduate Studies and Postdoctoral Affairs for review and final approval.
Graduate Studies and Postdoctoral Affairs (GSPA) reviews your application to verify admissibility."
