http://www.lslap.bc.ca/PDFs/18.pdf
"LOSS OF CITIZENSHIP
There are few reasons for losing Canadian citizenship under the current Citizenship Act. These are outlined in Part II of the Act. The exceptions are:"
"Before February 14, 1977, a person lost Canadian citizenship if he or she took out citizenship of another country because Canada did not allow dual citizenship. If a person lost his or her citizenship in this manner that person can now get it back through resumption. Since February 14, 1977 Canada has allowed dual citizenship;..."
http://www.cic.gc.ca/english/citizen/no ... ption.html
"As of May 5, 2005, people who lost their Canadian citizenship as minors between January 1, 1947, and February 14, 1977, can apply to resume their citizenship without having to become permanent residents and live in Canada for one year."