A massive influx of jobs and economic activity competing for your skill sets. Isn't this good?
Better plan this for areas already populated on the border. Where I live there are large cattle ranches.
NAFTA was supposed to do this. Manufacturing along the border cities (In Mexico) would employ people and no need for them to come here for work.
Unless your plan involves the workers being slaves they will still leave, come North, go everywhere they do now.