The Canada-United States Free Trade Agreement was signed in 1987 allowing free markets and fewer restrictions on trade. This agreement laid the foundation for NAFTA between Canada, United States, and Mexico, signed in 1994.
Like on the border on Mexico, the US tightened border security on the Canada-US border after the terrorist attacks on 9/11. While it delayed trading and decreased profits for a time, the US asserted the security was a necessary precaution to prevent terrorists from entering the country through its borders.
Canada has had its disagreements with the formation of NAFTA and extending the free trade agreement to Mexico. Canada has preferred to have a bilateral agreement with Washington. However, Mexico is Canada’s fourth largest trader and largest of Latin America.