Can you defer submitting a tax return due to illness?

You would have to contact the Canada Revenue Agency (CRA) to ask if you can get an extension. If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. If you are elsewhere, you can call 613-940-8495. This page has more ways to contact the CRA: Contact the Canada Revenue Agency

Please note: If the person has self employment income, then even though their taxes owing are still due on April 30th, their tax return (and that of their spouse) is not due until June 15 (actually June 16, 2025, since June 15 is a Sunday). Also due to issues with the capital gains forms, The CRA will grant relief in respect of late-filing penalties and interest until June 2, 2025, for Individual filers who have capital gains on their returns. So, you friend might not need an extension if they fall into either case.