Deadline to file 2017 tax returns for trusts and estates having December 31 as year-end https://www.canada.ca/en/revenue-agency/services/tax/trust-administrators/t3-return/when-file-your-t3-return.html  

For trusts and estates having non-resident beneficiaries, NR4 slips and summaries have to be prepared and filed by the end of March 2018. https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/t4061/nr4-non-resident-tax-withholding-remitting-reporting-2016.html#P273_24695