It depends. You would need to have Canadian source income to claim charitable deductions to a Canadian charity. If you have no Canadian source income, then contributions to Canadian charities cannot be deducted on your US tax return.
The following information comes from IRS Publication 526: "Canadian charities. You may be able to deduct contributions to certain Canadian charitable organizations covered under an income tax treaty with Canada. To deduct your contribution to a Canadian charity, you must generally have income from sources in Canada. See Pub. 597, Information on the United States–Canada Income Tax Treaty, for information on how to figure your deduction."
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