I hesitated to be more specific, but figured (probably wrongly so, should always be explicit when stating things like this) that it's implicitly obvious it's about the ~49th parallel border. In fact you can draw the line well below that border[0].

Another way to put it is that half of Canadian's population lives ~between Toronto and Montréal.

0: https://i1.wp.com/metrocosm.com/wp-content/uploads/2016/08/c...