It is my understanding that the profession of Physician Assistant is still somewhat undeveloped in Canada, and that most Canadian PA's have been trained and are employed by the Canadian Military. There is an emergent effort to organize national standards for certification of "civilian" PA's in Canada, the profession is in the process of being recognized "officially" by the Canadian Medical Association, and there is an organization named "Canadian Academy of Physician Assistants ", here
http://caopa.ca/english/
I assume you may want to contact them for additional information.
In the USA, the profession, training, and licensing of Physician Assistants is much more established. In California, for example, there is even a program, under the auspices of the California State Medical Board, to offer some sort of pathway for foreign trained PHYSICIANS (M.D. equivalents) to enter training and subsequent licensure as Physician Assistants. See here
http://www.physicianassistant.ca.gov/imp.htm
For general additional info re. the profession of Physician Assistant in the USA see here
http://www.paworld.net