663.3. For the purposes of section 663, an amount referred to in subsection 31 of section 104 of the Income Tax Act (Revised Statutes of Canada, 1985, chapter 1, 5th Supplement) regarding a beneficiary under a trust in respect of a taxation year of the trust is deemed to be income of the trust for the year that has become payable by the trust to the beneficiary at the end of that year.