How difficult, and what resources would I view, to prove an adoption in 1908?

[From Cathy] Firstly, are you sure it was an adoption? Before the Adoption Act of 1921, adoption was rare - guardianships were more common. If you don't know which it could be, I would suggest that you look up "Guardianships" in the Ontario Archives to start with. Beginning with the Guardianship Act (1827) and until the Adoption Act (1921), guardianships (child custody without the right of inheritance) were granted through the local Surrogate Court. While not listed in most Surrogate Court indexes, guardianship matters are recorded in Surrogate Court registers, and later, for some counties, in separate Surrogate Court guardianship books.

To identify series that contain these records, search the Archives Descriptive Database (Archival Descriptions search option) using the keyword guardianship* (including the asterisk), the name of the county or district, and the archival reference code RG 22* (including the asterisk). Alternatively, consult Inventory 22 Courts and related officers records, vol. 1, for instructions on how to identify and access these records.

If on the other hand you are sure it was an adoption, then it does make it harder (but not impossible) to find. The Archives holds no adoption files, only guardianship records. Adoptions occurring before April 8, 1921 were made through an Act of the Ontario Legislature and are extremely rare. For instructions on finding an Act, refer to Research Guide 207: Researching Ontario Bills and Statutes