@IceKitsune  
That’s narrowing down two of the simplest options that could’ve easily just been slipped in without anything changing, particularly for the episode.  
Sirens are canon in Equestria, that’s all well and good, but nothing of what happened there says “EQG happened after this”. It nods to the idea like Flash did, even if Flash was a last minute insertion and the Sirens were specifically in the script. Like they said “You know, we set up this idea that Starswirl did some stuff with the Sirens in this other series, lets animate that.” But without anyone in the scene specifically mentioning or whatever, it’s just nodding to the other series.  
The regular cartoon habit of saying “We’re not actively tying that to this, but you can think we are if you want, it makes no difference.”
 
I picture it like a pyramid sort of idea.  
The show is the main story.  
EQG takes some canon from the show.  
The comics take some canon from the show and EQG.  
But to each of them, whatever is below them isn’t canon to them.
 
The recent movie will probably go the way of EQG if nothing from it is shown in S8 onwards.
 
Course despite listing two of the simplest ways to make me think otherwise, there’s a whole goddamn list of ways to solidify the idea of them being canon to the show, but until they do so, they’ve really just left things open to say ‘Decide for yourself’.

@Brownee  
Why only those very specific things that you know they will likely never reference as they are going to have 0 bearing on the plot of any episode that isn’t a direct crossover?
 
See that is what you are doing, your narrowing your needed evidence down to something that you know they will never do as it would require a direct crossover between EQG and FIM to be even relevant to bring up, which you know is at best extremely unlikely.

@IceKitsune  

 
Pretty much that. Which is hardly anything.
 
Only reason I think like that is because cartoons make a habit of having movies for whatever reason and never reference them if the show continues after it, or has any aftermaths of situations in the movies. It’s very rare any of them do.  
A flashback that features the Sirens without saying anything about them is like a nod to EQG, in the same way Flash appearing without him or anyone else saying anything is.

@Brownee  
See this is why sometimes you can’t be subtle at all with things, and this inclusion isn’t even subtle at all really. How more explicit to you need it to be? What exactly would satisfy you that EQG is canon?

@cloudkicker108  
Kay. And? It was a flash back, one that didn’t even mention them by name or species, and the scene somewhat lined up with what their backstory apparently was. But showing without saying has just as much impact as Flash’s last minute inclusion.  
It’s a nod for certain, but it doesn’t flat out say “EQG stuff happened after this and is canon! Incoming Sunset!”

@Brownee  
I’m pretty sure the addition of Flash was a last minute thing and not a part of the script. After all, he had no bearing whatsover on the plot; you could easily switch him out with a random guard. The sirens, on the other hand, are specifically noted as the dazzlings in the script, and the scene in which they appear is more likely than not a retelling of the incident where Starswirl banished them to the EQG world.

@cloudkicker108  
Doesn’t really mean much. It’s practically the same as showing Flash in those couple episodes of S4.  
I mean I wouldn’t care if they were canon or not, but a visual nod isn’t really the same as acknowledging it verbally. Hell, mention the mirror while they were having that long talk about portals between worlds and whatnot. Or hell, showing the mirror in the background in the castle would probably be the only proper visual reference to solidify the idea.

@Xolcm  
 
For now…

Congratulations, you’re still powerless.

@Background Pony #9390  

 
And the Earth is flat.

@Background Pony #9390  
This anonymous troll has been making the same shit-post in the other threads.

@Background Pony #9390  
The sirens are explicitly referred to as the dazzlings in the script. Not to mention the coloration is identical. There’s no way EQG isn’t canon now.

EG still not canon. Only the sirens are canon.

It’s canon, and it helps establish the canon relationship between the human world of EQG and the pony world of FIM. Basically, Starswirl discovered the way to go between the two worlds, either by creating a direct portal like he did here or by fashioning a magic mirror that others could use.
 
The important thing to remember is that the process of going between worlds transforms the traveler. Ponies or pony-like creatures like sirens get transformed into humans when they go from the FIM side to the EQG side, and humans get transformed into ponies when they go from the EQG side to the FIM side. (This preserves the “no humans in Equestria” rule that Faust originally laid down when creating FIM.)
 
Why Spike got turned into a dog is a bit of a mystery, but Starswirl probably didn’t have any dragons to test his spells on, so chalk it up to randomness.

@darknessRising24  
Ok, but it`s still in EQG Short and cannot be as canon in FiM.

@Evil Emperor Proteus  
You need to calm down. Yes, BP is more likely than not wrong, but that’s no reason to lash out at him.

@IceKitsune  

 
You under estimate the power of delusion and denial.

@angrybrony  

 
They’ll just say it’s the other Sunset.

@Michaelsety  
Technically it is considering we’ve already been shown these characters in the main series. Not to mention the fact that Starlight herself has been shown in the eqg short.

@angrybrony  
It’s literally in the script for the episode though! You can’t make it any more canon than that, I don’t think it would be physically possible, it’s a showing of one of the events of the movies.

@IceKitsune  
it’s never over. sunset could pop up in the next season mench her adventures in EQG complete with flashbacks and poeple would still find some way to handwave it away

Let’s be honest, will magic mirror be appeared in MLP FiM or Equestria Girls humans will be appearing to MLP FiM?
 
Even it is already canon as covered comic book, but Equestria Girls is not explicitly canon to MLP FiM.

@Mojo  
Thank you leaks! Now, this stupid argument can finally be over forever. I mean it would have ended once we could ask the staff but at least this ends it earlier.

@Glim Glam
 
The episode script literally makes a point to note these are the exact same characters as the ones from Rainbow Rocks.