NEW YORK In a bid to kickoff a new era for DC Studios , James Gunn’s “ Superman ” opened with $122 million in U.S. and Canada ticket sales over the weekend, according to studio estimates on July 13. DC and Warner Bros. had a lot riding on “Superman.” While the Walt Disney Co.’s Marvel Studios has had its own share of struggles, the superheroes of DC have recently found mostly kryptonite in theaters. Films like “Joker: Folie à Deux,” “The Flash” and “Shazam! Fury of the Gods” all flopped. But “