Try the resources linked below for each of the following date ranges:
pre-1869: Try the Guide to Church Records for more information
1779 – 1858: Marriage Bonds, 1779-1858 - Upper & Lower Canada from the Library and Archives Canada
1786 – 1870: The District Marriage Registers Of Upper Canada/Canada West (no Midland District registers exist)
1858 – 1869: Ontario, Canada, County Marriage Registers, 1858-1869 (Ancesty Library Edition, limited access)
1869 – 1927: Ontario Marriages, 1869-1927 on FamilySearch
1928 – 1932: Marriage Records using the Archives of Ontario Microfilm Interloan Service.
1933 – 1936: Ontario, Canada, Marriages, 1826-1936 (Ancesty Library Edition, limited access)
1937: Closed for microfilming
1938 – present: Registrar General's Online Certificate Application (Service Ontario)
4 Volumes: Vol.1 (1869-1875), Vol.2 (1876-1880), Vol.3 (1881-1885), Vol.4 (1886-1890).
(no Midland District registers exist)
Family events such as baptisms, marriages and burials are key elements of genealogy and family history research. From early times to the present, these events have been recorded in church records and in other official documents. Library and Archives Canada holds a small collection of such documents, some of which are indexed by name.
— from the Library and Archives Canada website
Use the Search: Database link in the left menu to search the database.
Index to marriage records housed at Archives of Ontario in Toronto. Includes regular registrations, 1869-1927, and delayed registrations, 1892-1919.
An article from Global Genealogy explaining district marriage registers & district vital records of Upper Canada/Canada West, some of which are sold directly on the site.