The curtain’s up on KÀ — the fourth show in town from Canada-based but Vegas-lovin’ circus troop Cirque du Soleil — at the MGM Grand (from $99, 702-891-7777, It’s Cirque’s first production with a real plot — twins separated, a revolving stage, and pyromaniacal effects. Down the Strip, the new musical We Will Rock You puts 25 Queen songs onstage at the Paris Las ­Vegas (from $53, 877-796-2096, www.­ Let’s all join in on “We Are The Champions.”