International recruiting is not the same as immigration. Immigration serves a number of important political and economic objectives, but it is generally a slow process. If you need a radiologist to keep your hospital running effectively you cannot wait four years while applicants work through the immigration procedures. International recruiting is typically used as a way to hire temporary/contractual labour—people to fill a gap for a few months or a few years. For example, the oil sands projects will require plumbers, carpenters, electricians and roofers to build houses, offices and factories—but after the initial surge of construction is completed, foreign workers will return to their home countries.
Of course, international recruitment is not new. The scale of international recruitment is increasing as a consequence of globalization. Employers have become much more aware of the possibilities offered by international recruitment, and workers in developing countries actively look for jobs in the developed world.