What is the U.S.-Canada Data Exchange?
In order to increase the quality of trade data, the United States and Canada agreed to exchange trade data. Because import data has more scrutiny paid to it, each country uses the other's import data as their export data. U.S. reported exports to Canada are actually based on Canadian data on imports from the United States. Canadian reported exports to the United States are actually based on U.S data on imports from Canada.
The paper "U.S. - Canada Data Exchange 1990 - 2001" reads:
In July 1987, Canada and the United States embarked upon a grand experiment by signing a Memorandum of Understanding (MOU) to exchange import statistics starting with January 1990 data. From this date, the two statistical agencies would no longer base their bilateral export statistics on export declarations. Instead, they would rely on the import statistics of the counterpart country. Statistics Canada relies on American imports from Canada as compiled by the U.S. Census Bureau as the source of its export data. Likewise, the U.S. Census Bureau derives its exports to Canada from data on imports from the United States compiled by Statistics Canada. Because of the greater scrutiny paid to imports by the customs agencies in both countries, this exchange provides a more reliable measure of the bilateral trade. In addition, the reporting burden on exporters and forwarders in both countries was significantly reduced, as export declarations are no longer required for trade between the two partners. It was one of the first agreements between trading nations relating strictly to trade statistics.