Go to Foreign income slip, located under the Income Tab > Tslips > Foreign Income then all translates to getting the Foreign Tax Credit which is on line 405 of your tax return.
If needed refer to the links provided below for more information:
Line 256 - Other exempt income including prescribed international organization (such as the United Nations).
FTC - The U.S. withholding tax rate charged to foreign investors on U.S. dividends is 30%, but this amount is reduced to 15% for taxable Canadian investors by a tax treaty between the U.S. and Canada.
