The letter should show your name, address and the date of issue of your driving licence, its current validity - upto ------ ( what date , month and year ).
Signature of the Licence Issueing Authority, His Office Stamp.
It should be on the original Government Letter head.
If not in English it should be translated and attested by the Camnadian Embassy in your country.
A simple certification of the above contents in any form of words will do the job.
Mostly such letter may not work.
You may have to appear for the Examination for drivers licence, pay the fee and if passed you will get G1 licence. Again you have to pass a road test to get the G2 licence and if passed you will have to go for another road test too for G. There is mandatory time limits to get each grade (graduating licence).
If you are planning to settle in Ontario, for more details just go thru:
http://www.settlement.org/sys/faqs_detail.asp?faq_id=4000121
for other provinces you can get details from Ministry of Transportation websites
