How do I determine my withholding tax rate based on Canada's tax treaty with the United states?

The U.S.-Canada Tax Treaty was created to ensure that an individual isn’t taxed on the same income in both countries in the same year. 

A resident of Canada will have paid tax in Canada and therefore will not be taxed again on this income on their U.S. taxes. Usually the combined Canadian federal and provincial personal income tax rates are higher than the combined U.S. Federal and State personal income tax rates. In most cases, aside from filing with the IRS, taxpayers will not owe additional money.

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TurboTax Using the United States-Canada Income Tax Treaty to Reduce Double Taxation

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