Thing is, that first separation of Canadian citizens is made in 1947. (before that it was much easier for British citizens to get in and get citizenship). There was certain period of time, when Canada was not recognizing dual citizenship and most of those who emigrated ended up taking the other citizenship and renouncing Canadians.
You need to check all circumstances there. For example if your father has renounced his Canadian citizenship before you were born, then you cannot inherit it. Also check the law around the year 1947 (after WW2).
Good luck