Just apply a month or two before its expire date. They will send temporary extension which will be valid for a year (used to be 6 months). You are good.
It depends on your country of origin. If they give you 10 years it will be 10. But for some countries they issue 5 years. Also if you have your pr card they issue 10 years I heard.
You can show articles of course. And if there is something about you specifically you need to submit.
Also why did you wait until now to claim? Have you applied work permit, pr, etc in Canada and rejected?
Did they send to your home address physical work permit which is valid for one year? Or are you talking about the temporary extension they send after your submission?