You must have a SIN or ITN number to be able to file a tax return in Canada.
This Canada Revenue Agency (CRA) page has information on how to apply for a Social Insurance Number (SIN): https://www.canada.ca/en/employment-social-development/services/sin/apply.html
If you are not eligible for a SIN number, this CRA page has information on how to apply for a individual tax number (ITN): https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents-tax/in-outside-canada/apply-individual-tax-number.html