http://www.cic.gc.ca/english/helpcentre/answer.asp?q=748&t=22
If you already live in Canada, you have two options to become a permanent resident:
You can make an appointment at a Citizenship and Immigration (CIC) office near where you live in Canada. To do this, contact CIC’s Call Centre at 1-888-242-2100. You cannot call this number if you are outside Canada.
If your permanent resident visa (or one of your family’s) expires in two months or less, please tell the Call Centre that you need urgent processing.
If you are not able to make an appointment as set out above, you may leave Canada and return through an international airport or a Canadian land border.
When you arrive, a CIC officer will interview you, and grant you entry into Canada based on the information in your visa.
In either case, you will have to show the officer:
your passport, travel or identity document (including your visa sticker, if you have one), and
your Confirmation of Permanent Residence, permanent resident visa, letter of introduction or any instructions from the Canadian visa office, and
your proof of legal status in Canada, such as a valid work permit, study permit, temporary resident permit, or visitor document, or any immigration document you have (whether valid or not), or
proof of implied status (if you applied to extend your stay before it ended). Proof of this status may include:
payment receipt,
copy of your application to extend your stay,
printout of online application, or
proof of mailing.
Note: You must leave Canada, enter another country and re-enter Canada to become a permanent resident at an international airport or Canadian land border. If you need a visa to enter another country before you re-enter Canada, it is up to you to get the visa.
You will do these procedures at the first place you arrive in Canada. If you are travelling by air, make sure you have time before any connecting flight or other travel.
If you choose to leave and re-enter Canada at a land border, especially during the peak periods of weekends and holidays, you may have a long wait time for service.