The US government was already looking to go to war with Germany, so any greater kind of provocation could have done it (if not with the kind of shock effect and consequent boost to national resolve Pearl Harbour did). A while ago there was a thread about a US battleship being sunk and that might well do it. Or a regular Japanese declaration of war, if they're crazy enough. A Japanese expansion into Southeast Asia has lots of flashpoints even if they deliberately circumvent the Philippines and sooner or later, a Japanese ship or plane will hit something American.
It is hard to see how the US could *not* go to war at this point.