PARLIAMENT HILL—Montreal MP Thomas Mulcair threw the NDP leadership race into an uproar Wednesday when he suggested prominent contender Brian Topp is “beholden” to big unions and depicted himself as the little guy ready to stand up to union pressure in the party. The same day it was disclosed NDP MP Peggy Nash, a longtime executive with the Canadian Autoworkers’ Union and friend of Mr. Topp’s, was planning to throw her hat into the leadership ring.