Slav, which premiered last week at the Montreal International Jazz Festival, “bills itself as a ‘theatrical odyssey’ inspired by ‘traditional African-American slave and work songs.’ It also features a nearly all-white cast performing the music. Its director, Mr. Lepage, is white, as is its star Betty Bonifassi. … On Wednesday, the storm proved too much, and the jazz festival and Ms. Bonifassi canceled the show after only two performances.”