Section 105 of the Income Tax Regulations gives effect to paragraph 153(1)(g) in the context of payments to non-residents. The purpose of paragraph 153(1)(g) is to ensure that if the non resident recipient of a payment is liable to pay income tax in Canada, then there will be funds available in the form of a percentage withheld and remitted, to satisfy the obligation. R105 withholding is not the final tax amount. It is only a tax instalment, contrary to Part XIII (Tax on Income from Canada of Non-Resident Persons).
Subsection 164(2) allows for this instalment to be applied against any income tax owed by the taxpayer