Hello Nicola,
When you are a non-resident, it is useful (actually necessary) to obtain a Certificate of Compliance so that you can get as much money from the sale of your property.
Guide T4058 does explain how to proceed in obtaining this Certificate of Compliance (see page 8 -section starting with Procedures to follow)
http://www.cra-arc.gc.ca/E/pub/tg/t4058/t4058-09e.pdf
You would need to fill out form T2062: Request by a Non-Resident of Canada for a Certificate of Compliance Related to the Disposition of Taxable Canadian Property.
Without the Certificate of Compliance, the buyer and his lawyer will want to retain 25% of the funds from the proceeds of the sale of the property. If they do not do so, they could be held responsible for the 25% of tax that you, the seller should send to Canada Revenue Agency.
If you have any further questions on the above or need to obtain telephone numbers to the International Division of Canada Revenue Agency, do not hesitate to ask. I would be more than happy to locate these for you.
Here is the web link for the International Division of CRA
www.cra-arc.gc.ca/cntct/international-eng.html
P.S. Are you certain that, in the eyes of Canada Revenue Agency, you are a non-resident? Occasionally, you can be deemed a resident. Make sure you have established with certainty that you are in fact a non-resident.