Withholding tax credits have changed over the past few years. What is the agreement between Canada and USA related to how much can be claimed and how much must be applied for as a reimbursement?
In addition, keep in mind the effect of withholding in a registered account, such as an RRSP or TFSA. From taxtips.ca (emphasis mine):
There is no withholding tax deducted from dividends received on shares of U.S. corporations held in an RRSP, as per the Tax Treaty between Canada and the U.S., Article XXI paragraph 2(a). Sometimes, withholding tax (at varying rates, depending on the country) is deducted from dividends paid by foreign non-U.S. corporations, even when they are in an RRSP. These withholding taxes paid by the RRSP are not recoverable.
If shares in U.S. or other foreign corporations are held in a non-registered account or a Tax-Free Savings Account (TFSA), withholding tax will be deducted from dividends received. When the withholding tax is paid from a non-registered account, it can be partially or fully recovered via the foreign tax credit. Withholding taxes paid by the TFSA are not recoverable.
Thus, at this time, it might not make sense to hold foreign dividend-paying investments in a TFSA.
According the the Canadian-US income tax treaty this varies depending on the type of investment but the maximum is 15%. This can normally be claimed as a tax credit up to the maximum of 15%. If a company is withholding more tax than this it is possible to apply for a reimbursement of the difference:
Canadian residents seeking to reclaim overwithheld taxes may look to the procedures under U.S. Treasury Regulation Section 1.1461-2(a)(2) for reimbursement or Treasury Regulation Section 1.1461-2(a)(3) for set-off of the overwithheld tax.