There would be no civil registration of death as that did not happen until around 1869 in Ontario. Parish registration were even later ... 1960's. Now the Church may have the registration of whom bought the plot but until the 1960's no registrations of whom were in the plot was needed. When John (Bane) Dewar came out it may have been under the name McClure.
Were two of his sons Donald Dewar and James Dewar?