In the beginning all schools were religious, Catholic in French speaking and Protestant in English speaking Canada. When the French speakers and Gaelic speaking Irish showed up  in Ontario they had to make their own arrangements for schools, hospitals, fire services and local security. All those sainted hospitals were started by Quebec and Irish nuns. Later on the Italians, Poles and others added to Catholic numbers and this is when the province paid Catholic School Boards roughly 50% of the cost with the other 50% being collected from Catholic residents and businesses as local taxes. At one time the thought of Catholics attending the established schools was much the same as in the American South  where segregation was looked upon as being the way God wanted it. 
Organised religion is in decline and in the Public Schools the climate in the classrooms toward religion is quite frigid. The Catholic schools do accommodate Jews, Moslems and others where all are based on the "Book".