Minor nit ... the only province of the three that gets its requirement from the Constitution Act of 1867 is Ontario.  That act conglomerated Lower and Upper Canada (Ontario being Upper Canada at the time) Nova Scotia and New Brunswick.  All the other provinces were added with independent acts. AB and SK didn't even exist as legal entities when that was drafted.

AB and SK were added with the Alberta Act of 1905 and the Saskatchewan Act of 1905, respectively, and both of THOSE acts contain references to a catholic system in their respective provinces.