If you've got that much information about him, and if you know his age, date of birth, or approximate year of birth, that may be sufficient for the registration authorities to identify the correct birth registration for him, and if they can, you may be able to apply for a copy of his birth certificate.
If you've got his parents names, then you've got his original birth name, unless there's another aspect to this situation that you haven't mentioned.
http://www.snb.ca/e/1000/1000-01/e/apply-e.asphttp://archives.gnb.ca/Search/VISSE/?culture=en-CAHis parents, and depending on the time frame, possibly also him, should be listed on the 1921 census of Canada.
http://search.ancestry.ca/search/db.aspx?dbid=8991Oh, I just realised what your fundamental problem is, you can't link his first identity and his second identity by means of official documentation.
Well what about his numbers, his social security number or his national insurance number, or whatever the Canadian equivalent of those is.
Did he change those as well. ? That wouldn't be easy to do. Perhaps he changed his name, presumably unofficially, but if he did so unofficially, did he continue to use his original numbers, and also, what about any medical numbers. ?