Quebec and Ontario developed as Canada's economic heart because of the provinces locations a. on the major waterway linking the Canadian interior and the Atlantic Ocean.
b. along Canada's major railroad lines.
c. bordering the Hudson Bay.
d. in the southeastern corner of Canada near the United States.

Quebec and Ontario became Canada's economic heart because of their locations in the southeastern corner of Canada near the United States.

Explanation:

A is not correct because if it was the waterways that had the biggest impact then all of Canada would have been equally economically powerful and developed as the majority of the provinces and territories come out of water.

B is not correct because the major railroad lines have only managed to help to some point, but not be the crucial factor.

C is not correct because if that was the case then Manitoba and Nunavut would have been on the same level as these two, but that is not the case at all.

D is correct because these two provinces border the economically most developed part of the United States, and when taken into consideration that the United States is the biggest economy it just gives us a perspective as to how much this can influence the surrounding area and its economic development.