Need more specification to answer your question.
First, did you be accepted as PR in 2012 and you just miss the Card or your PR been refused ?
If you just miss the card, you will simply need to apply for a permanent residence travel document before you try to come back in Canada.
But you should check about : *
" When you are a permanent resident, you can live outside of Canada, but must live in Canada for at least two years in a five-year period. If you live outside of Canada for longer, you may lose your permanent resident status."
"Even if you don't meet the residency obligation, you are still a PR until an official decision is made on your status."
So if you didn't receive a notification saying that you lost your PR, you still are PR of Canada.
If you never been a PR in Canada, well you need to meet all the same obligation than the others persons would need to provide if they want to visit or immigrate in Canada from your country.
I hope it will help.
Here the links that can be helpful :
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=064&top=10
http://www.cic.gc.ca/english/newcomers/about-pr.asp