By this token, all written pairings are canon–no? MC and RO-A is also there in black and white, written by the same author, and is precisely what you read if you make that choice.
I get that some pairings can subjectively feel more canon than others. Especially if a reader leans into their role as co-creator of an IF - a framing that drives some authors nuts, but is one valid way of construing how IF works - the reader may feel that nothing with the MC can really be authorial canon. That character isn’t owned by the author. The NPCs are; so what they do when the MC doesn’t intervene feels like author-canon.
But while I think that or something like it is one way to read/RP these works, it sure isn’t the only valid way. Here you’re writing again as if your perspective is the obviously right one and authors should all see that, whatever they “feel” or “intend.”
My game has been accused of having a canon MC-RO pairing; the fact that the RO in question may end up with another NPC if you don’t go for them has (so far) never convinced anyone that the author didn’t intend the MC to get together with them. There are a whole lot of disgruntled non-fans out there who would take strong issue with the idea that the NPC-NPC relationship was in any way the author-canon pairing for XoR, even though it’s there in black and white. My intent is irrelevant in all this, death of the author yadda yadda, but there’s no single authoritative reader either.
PS - I’d thought I’d be arguing with JBento about their persistent refusal to see that yours is also a valid perspective-- but you keep saying provocative things about authors and I can’t resist replying. 