Hello and welcome.
There were some assisted emigration schemes to Canada. Some were settled as a community in an area, others moved where the work took them. 1840s and 1850s were decades of mass emigration.
You say your ancestors "ended up in Southern Ontario". Do you know if they started off somewhere else in Canada?
The pages on emigration on Irish GenealogyToolkit have advice and tips. Select Genealogy tab, then Emigration.
Forms and spellings of surnames weren't fixed. Mc/Mac might have been dropped or added according to personal preference or circumstance.