Well if we use Francis I, then there would be a war between France and The Habsburgs.
Absolutely.
Who the Prince Electors and minor German states would support is debatable.
That depends on the promises the respective side make. And of course they'll oppose the one who looks as if he could become the supreme winner of that struggle.
Nevertheless, this could become a major French-wank. Say France gets Franche Comte, Sundgau, Breisgau and large parts of the Austrian Netherlands and the Hapsburgs loose the crown of Bohemia to another German noble house. That's not entirely unlikely. But it gives France a so much better starting position for the next round of wars.
On the other side, even with far smaller gains of France, the Ottomans might break Hapsburg power once and for all, and then the French king/HRE will go crusading to liberate Vienna and Hungary from the infidels. That he'll also end with large territories in the East is merely coincidal...
OTL France lost nearly every war with Spain and the Empire(hell Francis I was even captured and help in Madrid!) but if he focuses solely of the low countries and the Empire, ignoring Italy, he might have a chance.
The war will be between France and the Hapsburgs. Since the Hapsburgs sit in Spain, Italy and the Netherlands, all those will be frontlines. also don't forget that it requires quite some powerbase to fight and loose repeatedly against a power that controls American gold and the trade of the Netherlands.