In this Rebels season 3 teaser, Ezra can be observed using the Force on an Imperial AT-DP operator. From the way he used the Force to turn the battle around, is it in line with the moral principles of the Jedi or is it skirting with the dark side?
As per the Mind Trick page on Wookieepedia:
Also known as dominate mind or control mind, mind control was the dark-side equivalent of the Jedi mind trick, though mind control was much more invasive. It took complete control of the mind(s) of the victim(s) affected by the power. Higher levels of mastery allowed more people to be controlled, though its effect on members of certain species with an innate immunity to mind tricks (such as Hutts or Toydarians) is unconfirmed.
What we see from Ezra in this trailer does not appear to be Jedi persuasion: Instead it is far more akin to the mind control described above, and is described as a Dark-side ability.
As for Disney Canon, I'm afraid I could not find any examples of this power being used before, so a definitive answer on whether the ability is associated with the Dark Side or the Light Side in the new Canon may not be answerable yet.
For my own speculation, I would class such an ability as Dark Side even under the Disney Canon. It is comparable in invasiveness to Kylo Ren's mind-reading in The Force Awakens. While Ren's ability isn't necessarily classed as light-side or dark-side either, it wouldn't be a stretch to say that such an ability is associated with the Dark Side.
EDIT: With the premiere of Star Wars: Rebels Season 3 I believe we have a fairly definitive answer from the episode. After Ezra uses this ability, Sabine asks him about it.
SABINE: When did Kanaan teach you that?
EZRA: He didn't.
If Kanaan didn't teach Ezra "that", then who did? In the following scene, Ezra communicates with the Sith Holocron that he retrieved from Malakor at the end of Season 2. It's heavily implied that he has opened the Holocron and communicated with it before.
HOLOCRON: Your anger gives you strength, gives you focus. You can see things clearly your friends cannot. Now, what else do you desire?
EZRA: They can't see. If they can't see, I must become stronger, more powerful. I will never let my friends get hurt again!
In another scene, Kanaan discovers that Ezra has opened the Holocron and they have this discussion (emphasis mine):
KANAAN: The Sith Holocron? You opened it?
EZRA: Yeah I opened it, so what!?
KANAAN: Ezra, you know only someone who uses the dark side can open this thing.
EZRA: Well, the things I've learned from it have really helped me!
KANAAN: You're using it?
EZRA: Well maybe you should too! You might actually learn something.
KANAAN: Ezra, do you have any idea how dangerous this path is?
EZRA: Everything I've learned has helped me win one battle after another. I'm using it for good!
KANAAN: Acting out of anger produces quick results, but it's a trap!
EZRA: Not for me!
KANAAN: I can't let you keep this.
So, since it is clear from Ezra's own admission that he did not learn the technique in question from Kanaan, and since it's known that Ezra has used the Dark Side of the force to open the Sith Holocron, as well as Ezra admitting learning things from it, I therefore conclude that Ezra learned the ability in question from the Sith Holocron. Since the Sith are by their very nature Dark Side users, it is far from a stretch to conclude that this is explicitly a Dark Side ability.
I have to say it depends... on the point of view ;)
If we take the expanded universe and old rpgs such a direct force use could be seen as dark side (in the d20 star wars rpg using the force to directly attack a living being was always seen as dark side regardless of the reason).
If we just take the canon then we have the films and comics and there Yoda once wisely says that "aggressiveness" is a way to the dark side. While staying calm and centered is the way of the light side. This can be seen time and again in the clone wars and rebels series and even in rotj when jedi use their powers either just defensively against living beings or even somewhat offensively. But never aggressively, more to avoid more bloodshed.
Luke slightly jokes Gammorean guards so that no bloodshed occurs when he passes by them (he did so calmly not because he wanted to hurt them but because he had to in order to not kill them).
Kanaan, Anakin, Ashoka, Yoda, Obiwan time and again throwing even living enemies with the force hurting them. Anakin is a bad example though as he was often driven by anger here. But the others while staying calm did so in the way of the light side. As they did so calmly not with lust for hurting others, or anger driving them but instead calmly deciding that no other way is there but to do that (or being driven by the force itself... depending on the statement each).
So all in all: Just canon: Using the force offensively is not per se a dark side usage of it. The intent (and cause of the use) is as (if not more) important than the exact application of the force.
that is MAJOR dark-sidage!! Using to force to directly influence somebody to kill another sentient being is NOT the Jedi way.
Jedi are peacekeepers, defenders, protectors. (Then again Erza has never had any formal training and has grown up knowing only war and strife and death around him)
Think of it as the way of the open palm vs the closed fist.