"Dumb and Dumber To", the sequel to the 1994 comedy that raised stupidity to an art form, led the U.S. and Canadian box office this weekend, taking in $38.1 million and outmuscling last week's winner, "Big Hero 6." "Hero," Walt Disney Co's animated story of a boy and his robot, settled for a close second with $36 million, according to estimates provided by tracking firm Rentrak. Director Christopher Nolan's space adventure "Interstellar" collected $29.2 million for third place. "Dumb and Dumber To" stars Jim Carrey and Jeff Daniels as dimwitted friends searching for