Complex sentence: Notably, the borders between Canada and the United States were officially demarcated; all land south of the Great Lakes, which was formerly a part of the Province of Quebec and included modern day Michigan, Illinois and Ohio, was ceded to the Americans.
Split into simpler sentences: Notably, the borders between Canada and the United States were officially demarcated. All land south of the Great Lakes, which was formerly a part of the Province of Quebec and included modern day Michigan, Illinois and Ohio, was ceded to the Americans.