I think so. If you had a Sue that was entirely in another part of the world, not interacting with the canon, it would be possible. For instance, a Harry Potter Sue who was in a school in, say, South America who was perfect, talented, angsty, beautiful, and had all the boys falling over her, but didn't break any established rules of how wizardry works, would still be a Sue but not touch canon.

Why a Suethor would come up with this I can't imagine.

A Canon Sue is a sue that doesn't damage the continuum. She's integrated into the story, and the canon is in a sort of symbiosis with her, so she doesn't tear the continuum to bits but also can't take over more than what she's written to take over.

Yes, a Tenth Walker could fall in love with Legolas without being a Sue; but it would probably take more writing skill than the vast majority of writers have--including the published ones.

If a non-Sue changes canon, the story is simply an AU.

I don't really think it's situation that makes the Sue, it's attitude. So, as long as the Tenth Walker is mildly low-key and believable, and non-Sueish, they wouldn't really be a Sue.

I don't think these are n00bish questions. I think it is important to ask questions like these.

I think you will find that, even among our community, what it takes to call a character a Sue varies. Some believe that if the character has Sue-ish traits then, whether they warp Canon or not, they are Sues. Others believe that Sue-ish traits are not as important as the Canon warping.

I personally believe that If it looks like a duck (Rainbow-colored duck in this case), sounds like a duck (musical quacking?), and smells like a duck (cookies...maybe)then it is a duck. This is why I believe the terms like Canon-Sue are not a bad thing. It is simply defining a character by the characteristics that they share with a specific group.

We don't mind ducks, usually. The issue comes when you find a duck in the desert (a canon where it does not belong). A duck in a desert is out of place, where a duck in a pond is right where it should be so we don't mind that it is a duck.

Your second question is also interesting. To use the same metaphor, if you are looking at an animal that doesn't have feathers, a bill, or webbed feet, it probably isn't a duck. That does not meant that if you put it in a desert (or even a pond) it isn't going to be out of place. It is possible for even non-Sues to warp canon.

So, if that made any sense then I am glad. If not, I will try to clarify it.

-Barid

To the former, I think not, mostly on a matter of definition - if an original character meets the criteria to be called a Sue, they pretty much have to affect the canon (and, the spelling is "affect" in this situation; just so you know). On the other hand, an original character who has a few potentially Sueish traits but isn't an actual Sue themselves wouldn't necessarily affect the canon - well, technically, any OC affects canon because they're not supposed to be there, but they could have an extremely minimal presence.

To the latter: If so, I would love to see it.
I highly doubt it. However, there are some exceptionally good OCs around, and even the most Sueish storyline could, possibly (in some cases extremely remotely), be wrangled into a good story by a writer who very, very, very skilled. Actually, I did once read a fic about a human girl - whom the author deliberately made as her avatar - who fell into Middle-earth, fell in love with Frodo, and married him, and it was well written. She wasn't a Tenth Walker, but she did manage to evade most of the cliche pitfalls. So yes, I'd say it's possible, but the chances of finding or being able to write one are probably something like two million to one.

All questions are good questions :)