Deleted scenes aren't not canon, they're just cut for time. For instance, during Lois' investigation in BvS, she visits Jenet Klyburn and gets information that helps her figure out Lex is the culprit and why Clark couldn't see the bomb. That's not non-canon because it wasn't in the theatres, especially since they bothered to keep it in for the DVD/Blu-Ray release.
Everything in the Ultimate Edition of BvS is canon because it happened, it was just trimmed for time (for some reason). Everything that happened in Justice League is canon.
Now, if the Snyder Cut is released, its canocity will be determined by the studios, not by the wiki. If we were to do that, this would be a fan site instead of a Fandom one.
Things that wouldn't be canon are things that are stated behind the scenes that don't coincide with the films. If a crew member reveals information about a movie, that is when a dispute can be made as to whether or not its canon - though we can always ask on social media to clarify
That doesn't prove the canon of the Ultimate Edition nor the canon of Suicide Squad's Extended Edition, and especially not Snyder's so called "Snyder Cut" of Justice League. Lois just got the info from a different, more unknown source during the actual theatrical movie. It hardly presents itself as proof this cut is really canon.
How does it not prove they're canon? They wouldn't release it to the public if they didn't want to go by either version. Furthermore, the differences in cuts aren't actually substantial, as UE and Extended Edition just include scenes they didn't put in the theatres. All these extensions are just that, extensions on the same story you saw in theatres.
If in the theatres its shown that Lois got her information from an unknown source, then why would it be non-canon if its explained that she got it from Jenet?? Its the same source, same movie, same ending, just a small detail that was better explained. Director's cuts aren't non-canon just because they're different from what's in theatres, especially since it's the exact same story.
However, due to the nature of the 'Snyder Cut', which was abandoned by WB, if it was released we'd have to go off of future installments to see whether or not it's canon by whether movies released afterwards retcon it. If it's released, and movies retcon it, then this wiki will acknowledge that the Snyder Cut is, in fact, non-canon to the DCEU.
If the movies don't retcon it, then it is canon. This is the only instance in which a released movie should be debated over, as everything up until now has not been changed, just elaborated on in the associated director's cut.
So by this logic, if a deleted scene was released to the public, it is canon?
The Snyder Cut doesn't seem to be a real thing. Even if it was, i doubt it was canon. Everything he worked on was always meant to be the first draft filming wise before the editing and reshoots. So i don't think anything there was ever canon.
Actually, Snyder had the movie shot and principle photography done, he just didn't have the reshoots he wanted yet or the vfx done.
But yes, deleted scenes are canon. Like I said, they're deleted due to runtime. Though some are delayed for pacing.
Then are not included in the story. The whole reason that deleted scenes are deleted scenes is because unlike all the other scenes in the movie. These ones are moments the film could go without in the film-makers eyes. The ultimate edition is literally just a collection of deleted scenes that were actually finished.
In terms of this Synder Edition for Justice League, while everything was finished. Touch ups need to be done. Extra shots for special effects tune ups. Editing for a shot that didn't make any sense etc.
Actually, it's the original, full version of the film. It's what Zack Snyder wanted to release in theatres. I haven't seen the Ultimate Cut (I don't have access to a Blu-Ray player, and it's not included on the DVD) so I don't have an opinion on its quality, but I've read enough to know that it's not a collection of scenes the director thought were non-essential.
I think we don't know if a deleted scene is canon or not until it's referenced or contradicted in another film. Wonder Woman (2017) had a deleted scene (meant to be a post-credits scene, I suspect) with Etta and the Wonder Men planning to recover a mother box, and that scene was referenced in Justice League (when Bruce mentioned that the British recovered a mother box at the end of WWI), confirming its canonicity.
Well it is the ones they thought were non-essential for theatre release. And if you ask me, that is enough for me to classify it as non-canon material.