So what will happen to my iCloud data after I cancel my iCloud subscription?

Nothing. If you use up more than the 5GB after your subscription is expired, our information, files, data, and photos will no longer update and you will not be able to make any more new backups until you free up your storage used to below 5GB or you purchase more storage, which I believe Apple has made it very cheap so I don’t see why you’d cancel it.

Lexxmech wrote:

So what will happen to my iCloud data after I cancel my iCloud subscription?

Anything you have stored over the complimentary 5GB will be deleted.