It doesn't appear that Canonical JSON does anything about redundant escape sequences in JSON. I'm still looking into it to be sure. This is a big part of the motivation behind the Son spec, and represents about half the EBNF: https://github.com/seagreen/Son/blob/master/son.ebnf#L19
For anyone else who knows of more JSON subsets, if you report them here: https://housejeffries.com/page/7 it would be really appreciated. I definitely don't want to do duplicate work.