Here's a video overview of Buddy MacMaster's influence. Thanks to @Raywells for posting it on the chat. Thanks to @KindaScratchy for the other link, which contains a lot of good links.
He was a part-time fiddler, retiring from his railroad job after 45 years. The video states that he was to Cape Breton fiddling what Bill Monroe was to Bluegrass.
He didn't usually "play the violin for free", but it seems that he played about a million dances. The video indicates that that is one thing that distinguished Cape Breton fiddling from other genres---that it stayed close to the origins of fiddling by being tied together with dancing.