Answer: Agriculture, better and more jobs, they are urbanized
Explanation:
Because in Southern Ontario and Quebec, or better said, Toronto and Montreal, is better for living because of the needs and jobs or careers of the people that are living in them.
They are urbanized and people who are looking for jobs or go to university are mostly wanting to live in those urbanized areas.
That is the main cause of their living in Southern Ontario and Quebec but there are also more, for example, in these provinces we can see fertile areas and they are allowing agriculture.
