Your vacation sounds exciting! I'm glad you're including Prince Edward Island in your special time away.
I would be sure to check out the Buzz online - our local arts and entertainment newspaper. They have the most up to date listing for all things music and entertainment. If you want a hard copy, they are free of charge and can be picked up at almost any restaurant or boutique.
You should have no trouble finding a ceilidh almost any day of the week somewhere on Prince Edward Island. A ceilidh for sure is guaranteed to give you toe-tapping to the fiddles!
You also happen to be coming during the Fall Flavours Festival - going on from September 4 to October 4, and there is an incredible array of culinary events, often paired with music. Check out the website to see the events that are happening while you are here, and if there is something of interest, make sure you book right away... those tickets sell fast! You might want to take in the PEI Shellfish Festival, running September 17-20 - in Charlottetown. Quite a bit of musical happenings with that event as well!
Another wonderful musical experience can be had at the Trailside Cafe in Mount Stewart. Located about 20 minutes from Charlottetown, this venue is a real gem for live music. The food also happens to be delicious. If you can make it to a show, you won't be disappointed - the eclectic decor and intimate atmosphere are a brilliant backdrop for the talented Canadian and East Coast artists that it hosts.
Trust that this gives you some choices.