Foreign tax credits
The tax treaty the United States hold with Canada is designed to protect US citizens from paying double tax, certainly to a large extent anyway. With low to medium incomes, the tax rate is roughly the same between Canada and the States whereas high-income earners will typically pay more tax in Canada.
Do I qualify for foreign tax credits?
As an American living and working in Canada, especially for high-income earners, usually the use of Foreign Tax Credits will be the best way to file.