CRA indicates that a non-resident trust can be retroactively (going back 5 years) deemed to have been resident in Canada if a non-resident contributor immigrates

A non-resident trust has resident beneficiaries with a current potential entitlement to receive income or capital and its contributor had made a contribution to the trust less than 60 months before becoming resident.

CRA indicated that in light inter alia of the lookback rule in s. 94(10), the trust is deemed to be resident for the five taxation years before the taxation year in which the individual became resident in Canada. Thus, the trust will be subject to interest and late-filing penalties for failure to have filed T3 returns (reporting its income for those years) and (where applicable) T1135 or T1134 returns for those years.

Neal Armstrong. Summaries of 29 May 2018 STEP Roundtable Q.14 under s. 94(3)(a) and s. 94(10).