CRA notes that it has no discretion to extend the one-year deadline under s. 164(6) for sustaining the post-death capital loss

After noting that CRA has the authority under Reg. 600(b) to accept a late filed s. 164(6) election, it also “noted that this does not change the requirement that the losses to which this election applies must have been incurred in the first taxation year of the estate.” After noting the Joint Committee submission to Finance that this one-year requirement should be alleviated, CRA stated that it “is prepared to work with Finance should they seek our views on this issue.”

Neal Armstrong. Summary of 2020 STEP Roundtable, Q.15 under s. 164(6).