When is the PoD? Butterflies, anyone?
1814 for Europe and 1774 for America. TL resume coming.
The first Congress of Vienna breaks down and Prussia & Russia (with the support of Murat's Naples) go to war against Austria, Britain, and Bourbon France because of the Poland-Saxony issue. In the middle of that war, Napoleon seizes the opportunity to stage his comeback and turns the conflict into a three-sided war, depriving the British and Austrians of critical support. Prussia and Russia screw Austria, Napoleon kicks Wellington's butt at Waterloo and wins some indecisive battles, but he's eventually vanquished by superior Russo-Prussian numbers. In the meanwhile, Britain is getting another butt-kicking in the War of 1812 because of a different PoD (the Canadian colonies join the ARW and the US, Washington accepts a third term and butterflies a 40-year Federalist dominance into being, and the Federalists build a very good US Army and Navy). Defeat at Waterloo brings down the pro-war Tory government and Britain sue for peace. Prussia and Russia dictate a one-sided peace at the Second Congress of Vienna.
Russia gets all of Poland but West Prussia, Finland, Galicia, Bukovina, and immediately thereafter evicts the Ottomans out of Europe, then annexes Moldavia, Wallachia, and Bulgaria, and makes Greece into an independent satellite and the Straits into a free zone. Balkan Muslims are expelled and resettle into the Ottoman Empire and South America.
Prussia gets Rhineland-Westphalia, Saxony, Hanover, and Bohemia-Moravia.
Because he's so successful, Tsar Alexander I maintains his liberal sympathies, and grants a constitution and the emancipation of serfs. Prussia follows his example, grants a constitution and some liberal reforms.
Murat keeps the throne of Naples and gets Lombardo-Veneto, Marche, Romagna, and later Albania and Montenegro. He follows a liberal course as well.
Austria loses all of the above, but gets Bosnia and Serbia. The shock of defeat freezes it into reactionary paralysis.
Netherlands and Scandinavia as OTL.
France loses Alsace and Lorraine (all of it) which is carved out as the independent Kingdom of Burgundy (part of the GC) and Corsica to Sardinia-Piedmont. Napoleon II keeps the throne (the victors reason out that the Bourbons are not that much better than Napoleon) under an Orleanist-Bonapartist regency. Napoleon dies a Russian prisoner. France follows a political course similar to the OTL July Monarchy, it humors the victors, makes a detente with Britain, tries to make Spain a satellite, and sets to build a colonial empire, starting with Algeria.
The USA get Rupert's Land (Quebec and NS are among the 15 original states), Northwest territory, Bermuda, Bahamas, Jamaica (Hispaniola was part of the Lousiana Purchase and French Caribbean was got in the Quasi-War), plus they stage a major intervention in the Spanish-American wars of independence, so Gran Colombia and Peru turn philo-US and later join the union.
Britain gets mostly estranged from continental Europe (although they gradually build an alliance bloc with France, Spain, and Scandinavia to contain the Prusso-Russian-Naples bloc in Europe and the Middle East), gives up North America, and goes to annex Argentina, Chile, Uruguay, and southernmost Brazil as British colonies. OTL 1820s-1830s internal reforms are anticipated by a decade or so. They may or may not aim to annex Indonesia and/or South China as colonies in addition to their usual India stuff.
Spain is wracked by its usual internal instability, loses the colonies it lost OTL to America and Britain, and it becomes a French satellite.
Liberal and prosperous Prussia and Naples become the magnets of German and Italian national movements. In two stages, from 1820 to 1830, the unification of Greater Germany and Italy occurs, with a mix of diplomacy and revolutions. The Habsburg Empire collapses, Germany gets Austria and Slovenia (it already had Bohemia-Moravia), Italy Trento, Kustenland, and Dalmatia, Hungary (with Slovakia, Transylvania, Croatia) emerges from the wreck as a German-Russian satellite. Uncertain about the fate of Bosnia and Serbia. The Serbians are the usual geopolitical mess to settle.
Poland may or may not stage its national insurrection (Russia is somewhat more liberal ITTL, but only up to so much), if it does Russia (with German support) donkey kongs it as usual. Romanians may or may not join them. Bulgarians are sufficiently content under Russian rule, and Greeks are busy dreaming of the day they reconquer western Anatolia and Cyprus.
In this big resettlement, the Belgian revolution may or may not still happen. I question what it happens if it does, assuming that the OTL solution is butterflied away from existence.
Moreover, with the German unification, the fate of Luxemburg (which still includes OTL Belgian Luxemburg), Burgundy, and Schleswig-Holstein is up in the air. Germany supports Netherlands about Belgium but claims the above stuff as German lands and/or parts of the old GC, Denmark and Netherlands want to keep as much of their stuff as they can, France wants as much of Belgium, Luxemburg, and Burgundy as it can grasp, Britain supports Denmark and France but it's not too keen about major French expansion in the Low Countries, Russia and Italy support Germany, Sweden supports Denmark, Spain supports France. All European powers are still wary to stage another general conflict 15 years after the Napoleonic Wars (although it would happen if Russia tries to snatch more Ottoman stuff).