The U.S. and Canadian economies are intimitely tied together and depend on cross border trade. Like I mentioned earlier, when the border was closed after 9/11, it shut down cross border trade. That shut down a good chunk of the industry in the mid-west U.S. and southern Canada. Stopping 'just in time' parts shipments shut down the entire auto and steel industries in 24 hours for starters. Shutting down the airlines was less costly to the economy than shutting down the border.