You may only apply to one of the Federal Tri-Councils: Canadian Institutes of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC), Social Sciences and Humanities Research Concil of Canada (SSHRC), in a given academic year.
You may hold a maximum of four years of funding from the federal councils at the post-graduate level.
If you are applying to SSHRC or NSERC, you only need to complete one application for a doctoral award. Top applicants for the doctoral award are offered the Canada Graduate Scholarships Doctoral (CGSD) award.
Applications for federal awards are made through the graduate departments and each department sets its own deadline. Deadlines and announcements are early in the fall semester.
NSERC is an agency of the Government of Canada that offers postgraduate awards of various types to assist students pursuing graduate degrees. Most, but not all, of the awards are restricted to Canadian citizens or landed immigrants. You can contact their web site for further information.