This is from Immigration Canada website:

"Since February 15, 1977, Canadians have been allowed to take foreign citizenship while keeping their Canadian citizenship."

In order to renounce your Canadian citizenship, you must complete the Application to Renounce Canadian Citizenship form, submit your photograph, original or certified copy of your birth certificate, proof of your Canadian citizenship, pay the $100 application fee and mail the application form and required documents to Sydney, Nova Scotia.

If you don't remember doing this, you are Canadian.