You don't need a computer to file your taxes.
Paper kits are provided by CRA and declarations can be submitted on paper by mail. Potential use cases being technology illiteracy, access to reliable internet connections just to name a few .
I'll go out on a limb here ... tell me if you disagree ... that if you file your taxes on paper, all that personal information will be quickly scanned and available in a database. The database of the site in question.
I say this because the My Account service allows a Canadian to check their balance, payments, credits, filing status, etc. It's there for anyone, ready to go, with whatever information the CRA has stocked it with. Your information, even if it started out on paper. It's pretty inconceivable that the CRA could function if the paper filings didn't soon end up in the same database as the e-filings.
Anyways, then at that point, your paper personal data is sitting right there behind the login of that same CRA site we're talking about. For your future convenience. Or leaking. Or hacking. And then we're back to ... "in the event of such occurrences, the Canada Revenue Agency is not responsible for any damages you may experience as a result."
I follow you train of thought and I'm wondering where the loophole would be. I mean if you file on paper you don't use the My Account service. How would the agreement acceptance occur ? Maybe the TOS could be interpreted as "being the holder of a canadian SIN, CRA gives you access to My Account".
In return for the Canada Revenue Agency (CRA) giving you access to My Account, you agree to abide by the following terms and conditions of use for this and all future uses of My Account:
https://www.canada.ca/fr/agence-revenu/services/formulaires-...