My grandefather was adopted in 1912 but ontario did not legalize adoption till 1921. Who would have handed adoptions before it was legalized and how would i get a hold of them ?

Was he adopted or was guardianship transferred from his birth parents to those who raised him? If it was a private 'adoption' you may find note of it in church records. If it was a guardianship transfer you'll have to seek out court records.