ok..
you meant you changed the major/course but still study same length of time and have a diploma/degree.
(if you elaborate your situation more, I would have understood correctly from the beginning)
don't think it would be problem, as long as you finished your course and have a diploma.
is your course/major name on your study permit?
If so, write a letter explain why you change your course with your PGWP app. (obviously your confirmation of degree would be under different program).
"is your course/major name on your study permit?"
i wouldnt know...because I have not landed in Canada yet...it is given to students upon arrival ...
otherwise, you do not need to inform that to CIC.