So? If you attacked France, what's the worst thing that can happen? Austria DoW's and takes a province? An uncored, wrong culture unlawful Imperial territory that it may or may not even have access to? Why would it want to do that when it could be expanding into Italy with those delicious universities? Poland and Denmark have other problems but if they're human-led they should be perfectly content to continue a phony war with you. And this is assuming all of them are player-run. An AI-led Denmark will land a huge stack in a province and try to siege it while the stack attritions away. Just wipe it out a few months later. Poland wouldn't ask for military access, you'd never see its armies before it white peaces out. So that just leaves Austria. An AI Austria should be pretty easy to bribe off with 25 ducats at the first hint of trouble. Heck, just do the usual way to kill AI stacks. Let the siege stack attrition away, move your armies away so it assaults, then go in for the kill. Now if they're the emperor... you may have trouble. You're probably better off just gobbling up the Low Countries to gain strength.
Or the more fun alternative way to end the alliance, actually duke it out. Or even worse, ally with the other side and gang up on France. Sure it sucks for France, but then he shouldn't of gone over the infamy limit. Or try to convince Poland to join up with you and flank Austria. Maybe it's just me, but every time I play a strategy game of any sort online, there's always one chucklefuck willing to backstab his alliance for the stupidest of reasons.