(2nd Monday in October) The first Thanksgiving Day in Canada after Confederation was observed on April 15, 1872, to celebrate the recovery of The Prince of Wales (later King Edward VII) from a serious illness. In the years thereafter, both the date and the purpose of the observance was proclaimed annually. In 1957, a proclamation was issued fixing permanently Thanksgiving Day on that day, thus eliminating the necessity of an annual proclamation. Unlike the American Thanksgiving, the Canadian Thanksgiving has had a number of purposes over the years, including cessation of war and disease, thanks and prayers for abundant harvest and continuing peace, and for “general thanksgiving to Almighty God for the blessings with which the people of Canada have been favoured.”
For more information, see https://www.timeanddate.com/holidays/canada/thanksgiving-day.