While climate change is widely considered to be one of the major challenges facing the planet today, the Government of Canada has yet to apply market-based instruments to abate greenhouse gas emissions. Canadian federalism, however, allows subnational governments to take action on climate policy. The purpose of this research is to understand why Canada’s three most populous provinces – British Columbia, Ontario, and Québec – implemented different carbon pricing policies after committing to a unified policy route under the Western Climate Initiative (WCI) in 2008. Since then, BC adopted a carbon tax; Québec followed through with their WCI commitment and now trades emissions permits with California; and, to date, Ontario has yet to price car...