My parents immigrated to Canada in 1969 and have expired British?
You would have to apply for citizenship before you can get a passport. Other answers give you the details. It will depend on when you were born, whether both parents were British citizens at the time, and if they were married. Their actual passports are less important than their status. Did they forsake British citizenship or are they dual citizens? It is their status at the time of your birth which is important here. I would suggest that you contact the nearest British embassy and ask for their advice.