CRA states that the residence of a dual-resident s. 94(3) trust generally will not be ceded to the IRS, but double taxation relief should be provided

Where a U.S. estate is deemed to be a Canadian-resident trust under s. 94(3) (or it has Canadian central management and control), Art. IV(4) of the Convention contemplates that the competent authorities “shall…endeavor to settle the [dual residence] question and to determine the mode of application of the Convention to such person.” CRA considers it quite unlikely that the Canadian competent authority would agree under Art. IV(4) that the trust was not resident in Canada. However, CRA indicated that the Canadian competent authority will accept requests from trusts that are deemed resident in Canada seeking relief from double tax - which could be provided unilaterally or following negotiations with the U.S.

Neal Armstrong. Summary of 13 June 2017 STEP Roundtable, Q.3 under Treaties – Art. 4.