TORONTO—Frank Mahovlich can’t pick a side. Who can blame him? The Hall of Famer won four Stanley Cup championships with the Toronto Maple Leafs—including the franchise’s last title in 1967—and two more as a member of the Montreal Canadiens in the early 1970s. So when the Original Six rivals open their first playoff meeting in 42 years on Thursday night, Mahovlich will simply be an interested observer. “I won’t be cheering for either one of them,” the 83-year-old said with a laugh during a phone interview with The Canadian Press. “I don’t want to make anybody upset. They’re both great teams and they treated me so well.” The Leafs and Canadiens used to meet regularly in the playoffs, tussling eight times between 1951 and 1967 before the NHL started to expand. “It was electric,” Mahovlich recalled of the atmosphere inside the Montreal Forum or Maple Leaf Gardens. “You stepped on …