I think Crisis Core tied perfectly with the original game, some things make more sense after playing it(Aerith denial being the most important of them).
I think it obviously canon while Maiden it's not.
Crisis Core was just to whore out Zack... who played such a minor role in the original game. (So much that I had forgotten about him and wondered who the heck he was when I first saw AC)
And if you want to take any of the compilation into consideration, you have to take it ALL and not just pick and choose. Like it or not Maiden was approved for publishing.
The compilation was also written in such a way that it could be interpreted into either fanbases favor.