I read my last reply and found it not quite clear. I would like to edit it.
The process is:
If you overstayed, that means your visa has been expired and you are still in Canada, you have two options:
1. Apply for restoration IN CANADA within three months after visa expired.
2. If u don’t apply for restoration within three months after visa expired, go back to your home country, wait the 6-month penalty passed, then apply again. The 6-month penalty is stated in the Immigration Law to punish your overstay, which means no approval to any visa application in the 6-month period. After 6 months, you are all good.
Btw, Always have a explain letter