British Columbia

That's not at all what it sounds like. I'm reading:

The original agreement between Canada and the United States regarding construction of the highway stipulated that its Canadian portion be turned over to Canada six months after the end of the war. In the postwar settlement, Canada did not pay for the highway itself, but assumed responsibility for its ongoing maintenance; furthermore, Canada compensated the United States for associated airfields, telephone lines, and other assets. The handover took place on April 1, 1946, when the U.S. Army transferred control of the road through Yukon and British Columbia to the Canadian Army, Northwest Highway System.

Canada and the US signed an agreement to make this happen. It also sounds like the road was virtually unusable during WWII