Sarah McLachlan’s ruminative tunes don’t immediately sound like the most obvious backdrop for a beer commercial. On Super Bowl Sunday, however, one of her songs will serve as exactly that. McLachlan’s sad, emotional 1997 song “Angel” will work as a call to attention during a humorous ad for Busch Light and is part of a bid by Anheuser-Busch InBev to develop a new consumer base for the longtime suds staple.