The Bruins finally learned the identity of their first-round playoff opponent after dropping a 4-2 decision to the Ottawa Senators on the TD Garden ice, and falling into the No. 4 spot in the Eastern Conference standings. The regulation loss meant the Bruins ceded the Northeast Division championship to the Montreal Canadiens, and will host the No. 5 seed Toronto Maple Leafs in a series that will begin on Wednesday at 7 p.m. at TD Garden. The Bruins have taken nine of their last 10 matchups with the Leafs and had won eight straight against Toronto prior to a March loss at the Air Canada Centre that saw backup goalie Anton Khudobin pulled from the game. The Bruins aren’t resting on the fact they’ve dominated Toronto over the last few years, though, and will instead be looking to find the upper register of their own game that’s eluded them in the 48-game shortened lockout season. “It’s always fun. It’s two of the biggest hockey markets going at it. Maybe not as classic a rivalry as a Montreal-Boston, or Toronto-Montreal, I guess,” said Shawn Thornton. “But I think whenever you have two Original Six teams going at it and they haven’t been in it for a while. ... I know they’re going to be pretty jacked up, up there [in Toronto].”