Canada stresses education and worker skills as requirements for immigration.
The United States favors family ties.
Canada gets the doctors and engineers and we get more bean pickers.
Many foreign students graduating from U.S. universities are unable to become citizens so they go to Canada where they are accepted based on their talents. As a result, many U.S. firms farming out some of their work to places like Vancouver because we lack the skilled workers.
You miss the point of why we allow most of the immigration into the US. The idea is that it is attempting to improve the lives of the American people. Bring people to this nation to do the unskilled less desired jobs and train actual Americans into skilled more desired jobs.
It is not that I agree that that is good for this nation (it is to me little short of a imported form of slavery that is resulting in a increase of apathy to the poor and minorities in general)....but nonetheless it is what America is currently doing.
Likewise: Do I think importing more educated people into America would be good for the American people? No I don't. Canada has a very low population and is in a VERY different place than is the US.