Final answer:
The Great Lakes St. Lawrence Lowlands were formed by glaciation, where advancing and retreating glaciers sculpted the landscape, creating the Great Lakes and depositing fertile sediments in the St. Lawrence River Valley.
Step-by-step explanation:
The Great Lakes St. Lawrence Lowlands were formed through various geological processes including glaciation and the resultant erosional and depositional actions. During the last Ice Age, glaciers covered much of what is now Canada and the northern United States. As these glaciers advanced and retreated, they sculpted the landscape, eroding the existing rock and soil. The melting glaciers left behind large quantities of meltwater which filled the basins carved out by the ice, creating the Great Lakes. Furthermore, the action of the glaciers left behind deposits of sediment, forming the fertile lowlands of the St. Lawrence River Valley. The area known as French Canada, which encompasses parts of Quebec and Ontario, boasts this mix of rich lowlands and significant bodies of water, a testament to the region's geological history.