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.