Canada-US Preclearance Arrangement | The Brian Mulroney Institute of Government

The United States and Canada have engaged in preclearance arrangements since the 1950s.
Preclearance entails an arrangement between two countries that allows customs and immigration officials from the country of destination to be located in the country of origin to deny or permit travelers and/or goods passing through the destination country.
From 2002-August 2019 Canada and the US conducted air preclearance through the Air Transport Preclearance Agreement between the Government of Canada and the Government of the United States (also known as the Air agreement) and the Preclearance Act of 1999.
In 2015 the two countries signed a new treaty called the Agreement on Land, Rail, Marine and Air Transport Preclearance between the Government of Canada and the Government of the United States (LRMA), which was a commitment made in the 2011 Beyond the Border Action Plan and officially entered into force in August 2019 to involve preclearance operations in all modes of transportations (land, rail and marine along with air which was already implemented).
Since previously the Air Agreement obligations were implemented in Canadian law by the Preclearance Act of 1999, the modernization of preclearance to create the LRMA also resulted in an updated Preclearance Act (2016).

Citation

Canada. Public Safety Canada. Preclearance in Canada and the United States. 2021. https://www.publicsafety.gc.ca/cnt/brdr-strtgs/prclrnc/index-en.aspx