I am fairly sure this is a non free package. It appears discord canary is just the name for how discord releases its test features, so I think this must be proprietary and certainly non-free. The link appears to take you to the main discord download site and the arch arm has it under a custom licence and no link to any source, as far as I am aware discord doesn't produce any kind of Free/Libre client.
Please correct me if I am wrong, or if this is here for another reason. I don't use it, but saw it on the recent updates/added list.

Thanks
ryry