I think this question would be much better phrased somewhere along the lines of "what proportion of Canada's population AT THE TIME did American Loyalists comprise?"

Trying to track descendancy over 200 years is hard and probably not informative.

To follow up with a question too basic for me to have ever found an answer - Were the 13 colonies and Canada something distinct before the Revolutionary War? Was it just that we (I am writing from Colorado) rebelled and some (mostly) British colonies didn't? New Brunswick and Nova Scotia do not seem excessively different from Maine from my arm's-length point of view. Would there have been any degree of 'us and them' in 1770 among those who would ultimately become the US or the Anglo parts of Canada?

By comparison, the imaginary line between the US and Mexico, or Haiti and the Dominican Republic, or 500 others, is more cut and dry.