On July 1, 1867 a few of the then provinces were brought together to form the Dominion of Canada. The first stamps issued to reflect this event (the large queens) did not happen until April 1, 1868.
I thought it would be interesting to display date cancelled stamps depicting April 1, 1868 or your closest one to that date. My own queens are a mess but I came across this one, Canada Scott#22, which I believe is Guelph April 3, 1868 (AP 3 68).
