From Finance Canada, a news release dated Dec. 29, 2011, "Harper Government Highlights Tax Relief for 2012":

The Harper Government today highlighted the following important tax changes taking effect in 2012:

• The final stage of the bold tax reduction plan introduced by the Harper Government in 2007 comes into force on January 1, 2012, when the federal general corporate income tax rate is reduced to 15 per cent. This type of broad-based tax reduction plays a well-recognized role in improving productivity and economic growth rates, thereby creating more and better-paying jobs for Canadians and raising their standard of living. As other nations face the prospect of tax increases due to unsustainable budget deficits and spending commitments, Canadians are benefiting from permanent tax relief that is broad-based and structurally sound.

Scott Hodge of the Tax Foundation provides more context in a blog post, "Canada Cuts Corporate Tax Rate to 15%, Lowest Overall Rate in G-7":

Canada can only revel in its lowest-tax status for a few months because on April 1^st, Great Britain will lower its corporate rate to 25 percent from 26 percent. Britain's rate is schedule to fall even further to 23 percent by 2014. Over the past six years, the only G-7 nations that have not cut their corporate tax rate are France, Japan, and the United States. Japan and the U.S. have combined corporate rate over 39 percent....

The drive by Canada and the U.K. to have the lowest corporate tax rates in the G-7 cannot be ignored. Canada is, after all, our largest trading partner, and the U.K. is our sixth-largest trading partner. Perhaps not so coincidentally, China - America's second-largest trading partner - also has a corporate tax rate of 25 percent, nearly 15 percentage points lower than the U.S. rate.

BRT President John Engler addressed the importance of lowering corporate tax rates while moving to a competitive territorial system in September testimony before a Senate finance subcommittee.