The Sonadow Christmas comic is one of those fun little side stories that feels like a gift to fans, but whether it's officially part of the Sonic universe is a bit murky. SEGA and the Sonic Team haven't ever clearly labeled it as canon, and it doesn't really tie into the main storyline. It's more of a festive treat—Shadow and Sonic trading snark under mistletoe? Yeah, that’s pure holiday fluff. Still, it’s got that classic dynamic, so if you squint, it could fit. Personally, I just enjoy it for what it is: a cute, non-serious romp that doesn’t need lore justification to be delightful.
That said, if you’re a stickler for continuity, you’d probably file this under 'what-if' material. The comic doesn’t reference major events or character arcs, and the tone leans into lightheartedness over world-building. But hey, canon or not, seeing these two rivals in a seasonal setting is worth the read. I’d treat it like a bonus episode—fun, optional, and full of charm.