I have not been able to confidently find Alexander Mitchell in the OPR BMDs on Scotland's People-
There is this result in the 1881 Canadian Census available on the LDS Family Search site, the only AM in Ontarion with a wife named Mary-
me: Alexander Mitchell Title: Gender: Male Age: 62y Calculated Birth Year: 1819 Birthplace: Scotland Marital Status: Married Occupation: Farmer & Bailiff Ethnic Origin: Scottish Religion: Free Thinker Head of Household: Alexander Mitchell Born During Last Year: Census Place: Collingwood, Grey East, Ontario, Canada District Number: 155 Sub District: B Division: 1 Page Number: 21 House Number: 752066 Family Number: 95 Digital Folder Number: 4466837 Image Number: 00108 Film Number: 1375897 Library and Archives Canada Film Number: C-13261 Household Gender Age Birthplace Alexander MitchellM 62y Scotland Mary MitchellF 55y Scotland George MitchellM 27y Ontario William MitchellF 24y Ontario Thomas MitchellM 20y Ontario Mary E. MitchellF 15y Ontario Malcolm MitchellM 13y Ontario Isabella S. MitchellF 11y Ontario Walter MitchellM 9y Ontario
What is the source of the Birth Date and location for Alexander; and for his Marriage to Mary?
It is nearly always useful if that additional information is provided.
Given his Birth Year, it clearly before Statutory Registration starting in 1855, so would appear to be from a Baptismal record; or from his own understnding.