The most storied rivalry in baseball is the Yankees and the Red Sox, despite what often seems like an annual exercise in disappointment in New England. Despite having a comparatively brief and less operatic history of losing to the Bronx Bombers than do the Sox, the Blue Jays were once the team to beat in the American League East. Now Boston and Toronto are again gunning for the top, led by a pair of young general managers. Theo Epstein of the Red Sox and J. P. Ricciardi of the Blue Jays represent a new generation of general managers, weaned on two decades of baseball analysis that started...