Canadians! What will they think of next? First socialized medicine, then . . . rock versions of sea shanties? Great Big Sea, who formed in Newfoundland in 1993, have been thrilling Canadians for nearly two decades by adding an edge to 500-year-old folk songs. A phenomenon in their own land, where YouTube comments such as “Sean McCann: Sexiest bodhran player in the world” seem perfectly normal, the group routinely wins Juno Awards and sells out “Ships and Dip” cruises, performing for a week on a cruise ship. They fare thee well on our shores on Tuesday, March 15, at the Mystic Theatre. 21 Petaluma Blvd. N., Petaluma. 8pm. $26. 707.765.2121.