It seems like URL’s to user profiles are not case sensitive.
For instance https://meta.discourse.org/u/DiscObOt works just as well as https://meta.discourse.org/u/discobot
But the canonical URL in the first variation is not canonicalized into the ‘official’ case of the username, possibly leading to duplicate content issues or the wrong variation being indexed.
We should normalize the username to lowercase username and force a redirect for the various obscure mis-cased usages similar to how we normalize topic urls / category urls.