TurboTax software will automatically provide the s. 20(11) deduction for income and foreign taxes reported on a T5, and will ignore any excess tax paid on a T3, as it should.
"When foreign property income (other than from real property, or from a trust) has had withholding tax in excess of 15% deducted, the excess can be deducted from income on line 232 of the personal tax return, “Other deductions”, as a s. 20(11) deduction. The excess foreign tax over 15% deducted under s. 20(11) reduces the amount of foreign non-business income which is used in the foreign tax credit calculation. If your foreign income is reported on a T3, then it is from a trust (such as a mutual fund or ETF), so this deduction does not apply.
Step 1: find the total of all of your foreign income, eg. from T5s and T5013s but not from T3s
Step 2: find the total foreign tax paid, eg. from T5s and T5013s but not from T3s
Step 3: find the 15% of Step 1
Step 4: line 232 is Step 2 minus Step 3
Thank you for choosing TurboTax.