If you were born in another country after February 14, 1977, to a Canadian parent who was also born in another country to a Canadian parent, you may need to take steps to retain your citizenship before you turn 28 years of age.
On April 17, 2009 the law changed to end the need to retain citizenship for many people. However, people born outside Canada who are subject to the retention rules and who turn 28 before the new law comes into effect must still take action to retain citizenship.
Also, if you were born outside Canada and your parent was a Canadian citizen when you were born, your child born in another country after the new law comes into effect will not be a Canadian citizen by birth.
http://www.cic.gc.ca/english/information/faq/citizenship/cit-proof-faq01.asp