there's no true ending, so all of them are canon honestly! gumdrop's is the easiest to get though i think.
Judging by your webcomics some endings are clearly not canon (assuming that the webcomics itself is canon).
1) according to the webcomics Syrup is still alive
2) she still runs her store.
3) the candy girl is alive.
In other words, we can rule out all bad endings.
As for good endings, I know following:
1)Syrup still doesn't know that her assistent has magical powers
The only way for Syrup to know it is to look inside the crystal ball. It means she didn't look inside the crystall ball. But refusing to look inside the crystal ball, as far as I remember, will always lead to the same ending - "Syrup end".
If my assumptions are right and I remember everything correctly it means that "Syrup end" is the true ending.