Tbh, I can't see how all of them aren't canon in some form. My guess is all 3 (excluding Aranea because its obiously canon) will take place at some point in the story timeline-wise. The events leading up to each DLC's climax will be canon, BUT, towards the end of each there will be a divisive choice that each character must make to change the events that DO happen. Each DLC should have a canon ending, but you can make a choice to get a different one. As I've said a while ago, I personally think all 3 will change the ending overall, but I don't think any of them take place at the ending specifically.
I'm thinking all 3 are between Chapters 13 and 14 for 2 reasons.
Reason 1: Placement in the story.
- Ardyn's can't be until this point, or it spoils the story. It will be a flashback type DLC I'm sure.
- Luna's will be at this point IF you are playing her while she is dead. Before this point, Noctis is supposed to be sad about her death and drab during the entire portion of Niflheim, anything before Chapter 12/13 makes zero sense. If its while she's alive, it can take place whenever before chapter 9, but I doubt this for Reason 2.
- Personally, I think Noctis's will be more of a dream-state sort of thing. It will take place during his slumber. Its the only part of the game where he "reflects" on everything and where he likely finds out more about Ardyn, Luna and what he could do to change things. I can't see it being before or after this point. He obviously did something while he was inside this dream state.
Then, depending on the conditions of all 3, they will change the ending in chapter 14 after playing it.
Reason 2: Square likely won't try and rewrite half the game if you can make a choice earlier than Chapter 13.
-IF any of these change the main games story in anyway. I can't see it being early in it at all (this is assuming these DLC are going to be integrated into the main game). That would result in changing stuff after these DLC occur, which is A LOT of work.
-Between Chapters 13 and 14 is good because it leaves only the timeskip and the climax, very easy things to change in the grand scheme of things. Nothing actually has to change in Chapter 14, just only when the actual confrontation with Ardyn and the "Wall" start.
Just my idea behind it.