Most stories are almost certainly canon
Generally speaking, all officially published Star Wars material is canon unless otherwise indicated. Supporting evidence for this book:
So I see no reason to assume that From a Certain Point of View is anything but canon within the current Star Wars universe.
But individual stories may have non-canon elements or be obviously non-canon
The content of the stories may or may not be canon if they are told by unreliable narrators who are bending the truth, which Pablo Hidalgo alluded to on Twitter:
Are the 'from a certain point of view' stories canon?
Some are. Some aren't. Some might be. Some might not be. Many of the truths we cling to depend greatly on our own point of view.
@StarWarsReference (the Twitter feed representing the Star Wars Reference Reddit) says that there are some stories that are obviously non-canon:
Most of the non-canon ones are pretty blatant (The Whills, a cartoon, Shakespearean Palpatine).
I imagine that more explicit details, or even a story-by-story analysis, will be available at some point.
This anthology is similar to the Legends comic series Star Wars Tales, which was originally presented as the sort of stories that people tell in-universe. Whether the content of the stories are true or false depends on the point of view, and intentions, of the narrator. And that one also had some ridiculous non-canon stories.
It's definitely not Legends
Again from Pablo Hidalgo on Twitter:
If not then why isn't it under the Legends line? Isn't that why Legends exists in the first place, to make it clear what's canon and not?
Legends exists to keep the back catalog in print without having new readers think it gives insights into current content.
It's a reprint label, basically.