The Ottawa River formed the border between Lower and Upper Canada.

The Canadas were merged into a single entity in 1841, shortly after Lord Durham published his Report on the Affairs of British North America.

The terms "Lower" and "Upper" refer to the colony's position relative to the headwaters of the St. Lawrence River.

As a result of the influx of Loyalists from the American Revolutionary War, the Province of Quebec was divided into two new colonies, consisting of Lower and Upper Canada.

The creation of Upper Canada was in response to the influx of United Empire Loyalist settlers, who desired a colonial administration modelled under British institutions and common law, especially British laws of land tenure.