Michels said:
Before 1946 Canada was a British Dominion,, thus your mother was a British national..
http://en.wikipedia.org/wiki/Canadian_Citizenship_Act_1946 http://en.wikipedia.org/wiki/Canadian_nationality_law
You might be one of the so called "lost Canadians" there were several subsequent laws to remedy the situation, you need to check if you fall onto one of them.
Yes, he does fall into one of them. In 2009, Canadian citizenship was returned to anyone who had become a Canadian citizen in 1947, and subsequently lost citizenship (by, say, swearing allegiance to the USA), and to their children in the first generation. However, this did not help people who never became Canadian citizens in the first place, such as a person born in Canada who became a foreign citizen before 1947. (The original poster's mother may fall into this latter category.) Bill C24, passed this year, made anyone born in Canada, even if they did not become a citizen in 1947, a Canadian citizen...and also their children in the first generation. So, the only way the OP is not a Canadian citizen is if his mother did a Conrad Black-type renunciation to Canadian officials.