The problem is all balance of power. Francispania is the most powerful state on the planet, bar none. The Dutch will hate it because it's mere existence is a standing threat to their independance. The Austrians will hate it because it'll be a threat to their dominance over Germany. The Germans'll hate it because, if there's one thing worse than being dominated by the Austrians, it's being conquered and ruled direct from Versailles. Ditto for the Italians. The Brits are going to hate and fear this massive new colonial empire the French have acquired.
You don't need an ideological difference to fear someone - just a threat.
Fear is a great motivator. But it is a question of what there is to be afraid of. remember, during the late 1500s and early 1600s, the Hapsburgs ruled directly or indirectly most of Europe, and just about all of the colonies. Many nations, particularly the protestant ones, attempted to fight back. But there was never any grand coalition against them for any signifigant period. Or during the 1520s, when the Ottomans pushed as far as Vienna by the end of the decade. The German nobles, faced with a threat more dangerous then any to them since the Mongols three centuries before, do nothing. On the other had, we see at the end of the 18th century, a major European nation, once a pillar of monarchism (that's where the term ancien regime comes from) become consumed in revolution. We see the entire social system which has stood in some form or other for decades be completly destroyed. Then this relative nobody shows up in their armies. He marches across Europe, and manages to throw down the massed forces of the Austrians, Prussians, and Russians, not to mention others which contribute to their coalition. He is not defeated in battle until 1809, and that is
Aspern-Essling. He does not truly start to collapse until the Penninsular Campaign and the Invasion of Russia, both of which tie involve 5-600,000 French and allied troops (for the record, Marlborough's army of 100,000 at Malpacquet was unprecedented in European history and effectivly unmanagable). He posed a threat to the institutions in place, and had bloodied to many noses to go unchecked.
This Bourbon franco-spanish union threatens the balance of power, but it htreatens only to realign it. And there will be powers which will see advantage in allying with it, or which will not care to join the alliance. Russia, Sweden, Prussia, and others all have potential gains they can make wit French aid. Sweden is trying to hold onto it's empire, Russia and Prussia are on the rise. All are far enough away that they will not immediately feel the blow of the French juggernaut, should it turn on them. And if they chose not to, they are far enough away that they cannot intervene against france (no russians crossing Germany to invade france, for instance). Other German or italian states may wish to throw off the domination of the Hapsburgs. And finally, all other things being equal, this alliance has the force to stand off much of Europe, in much the same way that the French did in OTL, albiet with mixed success.