there are 20 auto lanes of traffic at the san ysidro border because there's a lot of business.
many americans live in mexico and cross to work in san diego.
many mexicans live in mexico and work in san diego.
people on both sides cross frequently to do business and shop.
not to mention tourism.
and then there's the large american retirement community in mexico.
border transactions are only going to increase.
It's not only Canadians who cross that border; many of the terrorists come in that way. As do many illegal immigrants from European and Asian countries.