No single city sits at the geographic center of both Canada and the United States combined—the two countries span vastly different latitudinal and longitudinal ranges. However, if you consider the midpoint between the northernmost major Canadian city (Winnipeg, MB) and the southernmost major U.S. city on the Pacific coast (Port Angeles, WA), several North Dakota cities lie near that corridor:
These are approximations based on specific city pairs, not a true continental centroid. The concept of a "central point" depends entirely on which locations you choose to measure between.