My paternal grandparents are Canadian citizens.?
Quite possibly, if they obtained their citizenship BEFORE the birth of your father. Born in Canada or naturalized is the same for transmission purposes. Whats not the same is born abroad. Prior to 2009 it was sometimes/often possible to inherit citizenship from grandparents, if the stars lined up correctly. The government has a tool to help you figure it out: Am I Canadian? Youll note that in some cases, citizenship was retroactively restored, so what may have been the answer in the past may be different now (in a positive way for you).