Prospect, I don't think you need a lawyer - just a notarized description of the bike showing that it was originally a model sold new as a vehicle to be licensed in Ontario at the time. You can draw up the description probably better than a lawyer, and then swear to it for a Notary Public which is often found at municipal offices.
If you need a sample of the description, here's a copy of what I successfully used a few years ago for a CB160. (Its pretty simple.) I also had a copy of the original bill-of-sale to back-up the price I paid for it, but maybe that would not even be required.
-----------------------sample of notarized description, also signed by me------------------------------
June 1, 2006
This document is to itemize the particulars regarding a 1965 Honda motorcycle that was acquired without original ownership registration.
Make: Honda Motor Co.
Model: CB160
V.I.N.: B160-100xxxxx
Type: 2-cylinder motorcycle
Displacement: 161cc
Year of manufacture: 1965
Color: red
Purchased from: Xxxxx Xxxxxx (905-nnn-nnnn– Oak Ridges, ON)
Date of purchase: February 24, 2006
Purchase price: $200
...my name and signature...