わたしも先日Marriage Certificateもらいましたが、旧姓がのってますよ。結婚したら、相手の姓を手続きしなくても名乗れると解釈してます。
http://www.vs.gov.bc.ca/name/index.html
Using A Maiden Surname Or Married Name
After marriage, you can choose to continue using your own surname, or you can start using your spouse’s surname. Changing to your spouse’s surname does not constitute or require a legal change of name under the Name Act.
A spouse may use his or her surname before the marriage, at birth or by adoption. A spouse can also use the surname of his or her spouse by marriage.
At any time, you can use your original surname or maiden name again, and you do not need to apply for a legal change of name.
After a divorce, a person my use their name at birth or married surname.