As brought to the ATA's attention by the Livestock Committee, there has been discussions on the new regulations which went into effect July 1, 2021 between the US and Canada. Some resource websites and documents:
Cargo Programs | Transportation Security Administration (tsa.gov)
TSA Certified Cargo Screening Program
TSA___Certified_Cargo_Screening_Program_010308.pdf (scrlc.com) - 2008 document