Do I need to have a supervisor before applying to the MSc or MASc programmes?
No, you do not. When a student is admitted, an academic advisor is assigned to them to help them choose courses and thesis supervisor. Students are expected to find a thesis supervisor by the end of the second term. Sending e-mail to faculty does not help. Every faculty member receives several such e-mails and they have no means to evaluate them so they cannot commit. If an application is successful the student has 2 terms to find a supervisor, so sending mail in advance is waste of time.