We sold a lot of maple syrup to my husband's friends through his workplace in mason jars. I think that the three key things to remember are;
1. The jars must be new. No reusing allowed if you are selling them.
2. They must be labelled properly just like any other maple syrup bottle.
3. They have to be an acceptable volume/size. Seeing how most canning jars are pint or quart size, that shouldn't be an issue as those are the standard sizes for maple syrup bottles.

I haven't come across any regulations that would make mason jars unacceptable for selling maple syrup ...but I've only been looking at Ontario's regulations as that is where I am.

I like mason jars for friends and family, but I don't know how well they would go over with the public. It seems...well...cheap..when compared to the nicer glass bottles that syrup is traditionally sold in. But that's my opinion.