Turns out their is a dispute about this. Her are some notes from Wikipedia.
"The ranking for world's third largest country is disputed due to (1) conflicting information from different sources; and (2) differing methods on how land and water areas are calculated.
The
Encyclopædia Britannica lists U.S. as the world's fourth largest country (after Russia, Canada, and China) with a total area of 9,526,468 km2 (3,678,190 sq mi).
[7]
Other figures: The UN figure of (9,629,091 km2 or 3,717,813 sq mi) includes coastal waters, but not territorial waters.
[8] The CIA
World Factbook fiqure of (9,826,675 km2 or 3,794,100 sq mi) additionally includes territorial waters.
[9]
The
water area of United States includes all water categories:
inland waters,
coastal waters, and
territorial waters."
I think the real question is whether the Canadian figure includes territorial waters. Does anybody know?