When I went out to the U.S. my prospective employer had to apply to the State Dept. of Labor (Nebraska in my case) with tons of paperwork to show that they had tried to hire a U.S. citizen/resident alien locally and been unable to find anyone suitable. Then the whole file went to the local INS office and finally over to the U.S. Embassy in London.
The whole process took almost 12 months to complete! That was an application for permanent residence (i.e. to get a "green card"), so it may be a little quicker and easier for just a work permit. If I recall correctly from the paperwork I had, it may also be quite a bit simpler for Canadian citizens.