CRA requires that you report "all income" you earn. If you earn "casual employment income" you can report it as "Employment Income not reported on a T4", as long as that amount does not exceed $3,500. If you exceed $3,500, you will then need to report this income as "Self Employed" income and possibly pay CPP contributions on it.
https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-re...
