The Canadian prairies were not entirely unknown even in the days of New France. As early as the 1730s a family of explorers headed by Pierre Gaultier de Varennes, sieur de La Verendrye, began a series of overland explorations far to the west of Lake Superior. Their travels carried them into what is now the western United States, perhaps as far as the foothills of the Rockies. They visited Lake Winnipeg, the Red River, the Assiniboine River, and the Saskatchewan River as far upstream as the fork formed by the North and the South Saskatchewan.

The posts of the Hudson's Bay Company had given England a preferred jumping-off point for exploration of the Canadian west. An expedition under Henry Kelsey explored the territory between York Factory and northern Saskatchewan in 1690, long before the journeys of the La Verendryes. In 1754 Anthony Henday traveled from Hudson Bay as far as the foothills of the Rockies, reaching a point near the site of present-day Red Deer, Alta. Another Hudson's Bay Company trader, Samuel Hearne, discovered Great Slave Lake in 1771, and by descending the Coppermine River to its mouth, he became the first white man to reach the Arctic Ocean by land. Although the Rockies still barred the overland route to the western ocean, the Pacific coast of Canada was visited by sea in 1778, when Capt. James Cook explored the northwest coastline from Vancouver Island to Alaska.

In 1783 a group of Montreal merchants founded the powerful North West Company. Not only did the new fur-trading company provide sharp competition, but its trappers explored large parts of the previously unknown expanses of the Canadian west. In 1789 Alexander Mackenzie (one of the Nor'westers) followed the river which now bears his name from its source to the Arctic Ocean. Disappointed because he had not discovered a route to the Pacific, he set out on another expedition in 1792. After a strenuous journey over the most rugged country on the continent, Mackenzie and his companions at last crossed the Rocky Mountains to reach the Fraser River in 1793. From the Fraser they portaged to the Bella Coola, which they descended until they sighted the long-sought western sea. Only a few weeks earlier Capt. George Vancouver had explored the same part of the Pacific coast by sea.

Mackenzie's journey was the first made across the continent in either Canada or the United States. In 1808 the Fraser River was thoroughly explored by Simon Fraser, after whom it is named. In 1811 David Thompson completed his exploration of the Columbia from its source, in southeastern British Columbia, to its mouth, in present-day Oregon.