It works both ways; if America doesn't want tourists and business people crossing the border, then we will spend our time and our money elsewhere.  In the age of the Internet a lot of business can be conducted virtually, and there are many wonderful places for tourists to spend their money.

The other thing is, the United States often drew the best and the brightest to their universities and cutting edge research facilities.  This is changing and Canada stands to benefit tremendously.  So give us the best and the brightest whom you don't want because they are not "our kind of people".  

America's loss will be our gain.