Take Note: Seafarers from Australia, France, Georgia, Norway, Australia, Panama, Brunei, Jamaica, Philippines and Ukraine can work on Canadian flagged vessels, if they have valid STCW certificates which can be endorsed by Transport Canada.
Link: https://tc.canada.ca/en/marine-transportation/marine-training-certification-individuals/request-canadian-endorsement-attesting-recognition-foreign-certificate-through-reciprocal-arrangement#toc2Begin endorsement process with Transport Canada and have all your STCW certificates ready. Keep in mind that you will need an employer for the process to be completed at 100% so they can assign you certain tests + your medical exam so TC can finally endorse you and your certificates. It will allow you to work on Canadian flagged boats. Ukrainians with diplomas obtained in Russia will not be endorsed by Transport Canada.
Documentation for endorsement with Transport Canada: https://tc.canada.ca/en/marine-transportation/marine-training-certification-individuals/request-canadian-endorsement-attesting-recognition-foreign-certificate-through-reciprocal-arrangement#toc5
Document to fill (PDF formats): https://tc.canada.ca/en/marine-transportation/marine-training-certification-individuals/request-canadian-endorsement-attesting-recognition-foreign-certificate-through-reciprocal-arrangement#toc4
Transport Canada email address to send filled forms for endorsement: RecognitionofCertificates-Reconnaissancedesbrevets@tc.gc.ca
Have your work permit / visa
Hiring season on the East Coast of Canada begins at the middle/end of the month of march and ends in october. November-February is dead season because sea locks in the seaway are locked for maintenance while thick ice covers all water and slows down boats in the Saint-Laurent river and in the great lakes. You can try your luck during dead season (or all year long) with BC Ferries on the west coast: https://www.bcferries.com/our-company/bc-ferries-jobs
Keep an eye on sea jobs on https://www.jobbank.gc.ca/home.