I have a PoD for this scenario as part of my United States of the Americas and Oceania TL, although in a slightly different form that you imply (Napoleon plays a part).
During the Congress of Vienna, Russia and Prussia come to blows with Austria, Bourbon France, and Britain over the Poland-Saxony plan. Murat has an epiphany and sides with Russia and Prussia. While the former allies are fighting, Napoleon stages his comeback, and turns the war into a three-way fight. This wrecks the chances of Austria and Britain. Austria is steamrolled by the Russo-Prussians, who also take Hanover. Napoleon crushes the British at Waterloo (no Blucher to save Wellington) and takes the Low Countries, however after some months of fighting, he is vanquished by superior Russo-Prussian numbers. The war government in Britain, also reeling by the defeats in the Americas (ITTL Canada sided with the Rebels in 1774, owning to an oppressing Quebec Act, and the Federalists remained in office in the early 1800s, building a much better US military, so America kicks Redcoat butt in Rupert's Land and the Caribbean in the War of 1812) collapses and Britain pleads peace.
At the reconvened Congress of Vienna, Russia, Prussia, and Naples dictate peace:
Russia annexes Finland, Congress Poland, Posen, Krakow, Galicia, Bukovina, and gets free hands to do as it pleases with Turkey. In a few years, it crushes the Ottomans, annexes Georgia, all Armenia, Moldavia, Wallachia, Bulgaria, and Vardar Macedonia. Greece (with Thessaly, Aegean Macedonia, and Crete) becomes a Russian vassal. Austria is allowed to get Bosnia and Serbia.
The Straits become a free zone under the control of the powers.
Prussia annexes Rhineland-Westphalia, Saxony, Hanover, and Bohemia-Moravia, and becomes the unquestioned leader of the German Confederation.
Murattian Naples gains Lombardy and Venetia. Tuscany, Parma, and Modena are united as the Kingdom of Etruria under the Bourbon-Parma dynasty. Savoy-Piedmont includes Nice, Savoy, Piedmont, Corsica, and Sardinia as the Kingdom of Sardinia. Since Orthodox Russia and Protestant Prussia don't care as much about the territorial integrity of the Papal States, Ferrara and Bologna are given to Etruria and Ravenna, Romagna and Marche are given to Murat to build a land connection between his northern and southern possessions. The Pope keeps Umbria and Latium. Naples also annexes Albania and Montenegro when Russia defeats the Ottomans.
France loses Alsace and Lorraine to the newly created kingdom of Burgundy, which is given to the former king of Saxony, and Nice, Savoy, and Corsica to Sardinia. However it keeps young Napoleon II on the throne (the victors distrust the Bourbon as much as Napoleon I at this point).
Austria is made to renounce its Imperial title and becomes the Kingdom of Austria. It loses Bohemia-Moravia, Galicia, Bukovina, and all Italian possessions, but keeps the rest.
Made confident by his great successes, Tsar Alexander I concedes a moderate liberal constitution, and his Prussian and Neapolitan allies follow his example, as does Napoleonic France. Liberal policies start all four countries on the way to economic boom and sweeping industrialization. Prussia and Naples become a liberal-nationalist magnet for the other German and Italian states (including Austria).
In the early 1830s, liberal-nationalist revolution sweeps Germany, Austria, and Italy. Prussia unifies Greater Germany, Naples unifies Italy (including Trento, Kustenland, and Dalmatia), Hungary became an independent Kingdom with Slovakia and Transylvania and a federal union with Croatia-Slavonia, a client of Germany, Russia, and Italy. Bosnia and Serbia became a kingdom in real union with Hungary. With support by the liberal great powers (especially France), the liberals win the civil wars in Spain and Portugal. The Pope and the Curia flee to Iberia when revolution sweeps Rome, and support the reactionaries in the civil war and across Europe, so the liberal great powers put them under undeclared house arrest as theocratic subversive troublemakers. This provokes an unofficial schism between liberals and conservatives in the Catholic Church.
Otherwise of their cooperation about the Iberian and Papal messes, the great powers remain locked into a Cold War, the Eastern Alliance of Russia, Germany, Italy, and Hungary squared against the Western block of Britain, France, Spain, and Portugal, up into the mid 1850s.
Germany snatches Schleswig-Holstein from Denmark in a quick war. This spurs Denmark, Norway, and Sweden to unify in the Scandinavian Confederation.
The Ottoman Empire, teetering on the brink of collapse, sees the secession of Egypt, which gains Sudan and Hejaz. France colonizes Algeria, Germany colonizes Morocco, Italy colonizes Tunisia and Libya.
Britain, reeling from the defeats in North America and Europe, focuses on rebuilding an Empire, and snatches Chile-Argentina-Uruguay from Spain, western Indonesia from Netherlands, and starts forcing its penetration in China (soon followed by the other eager great powers).
The USA, in the meanwhile, has been steadily expanding with intervention against Spain on the side of the South American revolutionaries (that made them strongly pro-USA), and the various victorious wars against France, Britain, and Mexico. Long Federalist political dominance up to the 1830s led to strong investments into internal infrastructure, industrialization, and the military, which substantially accelerated US economic development and the colonization of the West (as well as making America a military power to be reckoned). On the eve of the American Civil War the USA includes all North America (except UK NFL & Vancouver island, Russian Alaska, southern Mexico & Central America, which are US protectorates for now), Colombia, Venezuela, Ecuador, Peru, Bolivia, the Guyanas, Hispaniola. It is locked into a strategic rivalry with Britain over British South America.
The American Civil War happens in 1856, with the secession of the slave-holding Southern NA and Caribbean states against the Northern NA and South American antislavery states. Intervention of the Western Alliance on the side of the Confederacy brings the Eastern Alliance on the side of the Union, and the ACW turns into the first World War.
