Great Lakes Winter Commerce Act of 2020 This bill directs the U.S. Coast Guard to conduct icebreaking operations in the Great Lakes in accordance with specific performance standards. Specifically, the Coast Guard must keep channels and harbors in the Great Lakes open to navigation not less than 90% of the hours that commercial vessels transit ice-covered waterways; in a year in which the Great Lakes are not open to navigation because of ice of a thickness that occurs on average only once every 10 years, keep channels and harbors open to navigation at least 70% of the hours that commercial vessels transit ice-covered waterways; and coordinate Great Lakes icebreaking operations with operators of commercial vessels. The bill prohibits the Coast Guard from breaking ice in Canadian harbors or bays unless it meets these performance standards during such activity. Such prohibition may be waived on a case-by-case basis upon approval by the Department of Homeland Security and notification to Congress.