As ststed on CIC website and I quote :
" Impact of length of program of study in Canada and the length of the work permit
A Post-Graduation Work Permit cannot be valid longer than the official length of your program of study in Canada. For example, students graduating from a four-year degree program might be eligible for a three-year year work permit. Students graduating from an eight-month certificate program would only be eligible for a work permit of eight months.
If the official length of your program of study is:
less than eight months
you are not eligible for this program
less than two years but more than eight months
you may get a work permit for a period no longer than the length of your program of study (for example, if you studied for nine months, a work permit may be issued for a period of nine months)
two years or more
a work permit may be issued for three years".
Hope this will help