CRA indicates that waivers generally cannot be used to extend the 6-year period for claiming a FTC under s. 126(2.21)

Where an individual, who had been resident in Canada for over five years, realized a capital gain from the deemed disposition of non-Canadian real property under s. 128.1(4)(b) on emigrating from Canada, he would be potentially eligible under s. 126(2.21) to claim a Canadian foreign tax credit for foreign taxes that become payable on the gain that accrued in Canada, provided that this credit is assessed within the extended reassessment period of six years following the emigration year. Can this period be extended by filing a waiver with CRA? CRA stated:

[I]f any of the circumstances to support the deduction under subsection 126(2.21) … (e.g., disposition of the property and/or foreign taxes paid) are present within the statutory assessment period referred to in paragraph 152(4)(b) … it may be appropriate for the Minister to consider a taxpayer’s waiver request for the emigration year to allow the Minister sufficient time to review and process any potential reassessment for this deduction beyond the aforementioned reassessment period.

This seems to be saying that a waiver can be useful in giving CRA the time to process the FTC, but is not a mechanism for getting the FTC for foreign tax that is not triggered until, say, 20 years after the emigration year.

Neal Armstrong. Summary of 11 October 2017 External T.I. 2016-0660421E5 under s. 152(4)(b)(i).