I got visa for a pg diploma, after msc, on my second application.
Strong SOP is the key.
Reasons for initial refusal: "I am not satisfied that you will leave Canada at the end of your stay, based on your family ties in Canada and in your country of residence"
"I am not satisfied that you will leave Canada at the end of your stay, based on the purpose of your visit"
1st application, apparently, wasn't convincing enough, so I modified my SOP to be more convincing. Particularly, addressing the concerns they noted.
Good luck