Also NAL, but I would say it very much depends on the law in which-ever jurisdiction it gets tested in - which might be the one you are in, the one Canon are in, or somewhere else entirely.
Some legal concepts such as "fit for purpose" as defined in the UK's Consumer Rights Act (2015) certainly seem relevant here, but that states that companies should offer replacement or refund. Note the word refund, not recompence, is used: Canon may be required to repay you in full everything you paid for the service. All £0.00 of it.
> i.e. people paying Canon to host their photos
Is this the case though? Several other comments have mentioned it being a free service. https://image.canon/st/en/faq.html states that too. Unless there is a non-free option too.
> but when a service is advertised as being ideal for storing your work or photos
I'm not sure what it is advertised as, but that doesn't seem to be what the service is intended for.
Reading other parts of the FAQ it seems that the service is intended as a transfer agent, with the convenience of online storage being a useful side effect. Quoting the FAQ: "Image.canon is designed to ease your imaging workflow – whether you are a professional, enthusiast, or casual user. Wirelessly connecting your camera to the service allows seamless forward of images not only to your computer and smartphone devices but ...". The implication I'm making being that they can just argue that their service is designed to move images around your devices and the user should have been backing them up from there.
Users might try to argue false advertising if "fit for purpose" doesn't fly because of the purpose being defined differently. But good luck funding such as case against the lawyers that Canon can afford. It would have to be a class-action or similar, unless some government body takes the issue up (which from the users PoV will effectively be the same, and the best they'll get is a small voucher for a few £ off future Canon offerings). That is what a lot of things like this boil down to: legally enforceable sometimes doesn't exactly mean legal, it sometimes means "can be enforced by having a better legal team than the little guy"!