The Seven Year War aren't a bad POD.
So let's say that Austria receive Silesia back and Mark and Cleve
France get some border modification in the Austrian Netherlands, and most of their colonies back
Russia get (East) Prussia, which they trade with Poland for the territories Russia got in the first partipation.
Sweden get Prussian Vorpommern and Bermen-Verden
Saxony get the Kottbus enclave and support from Austria and Russia to make the Polish throne heritable.
Brandenburg has just cut down a notch, and Saxony has been strengthen.
After the war we Peter becoming Emperor of Russia, he turn toward his obsession with the downfall of Denmark and allies with Sweden (which hasn't been alienated by his peace with Prussia), the Russian-Swedish alliance defeat Denmark and the Oldenburgs are forced to give up Schleswig-Holsteinto Russia while Sweden receive Norway against giving up Bremen-Verden. Peter are couped a few years later (for rather stupidly having strengthen Sweden). After the coup Frederick August are granted the Duchy of Schleswig-Holstein (and Bremen-Verden). With that Denmark and Russia are out of Germany.
A few years down the road we see the War of Bavarian succesion happening. Through instead of Brandenburgm, Saxony turn out the leader of the anti-Austrian alliance. Of course Saxony even a strengthen in union with Poland one are no Prussia, and the war get dirty, Catherina invades Poland, France join the Austrian side against gaining Flandern. UK join against the French. The war turn into another Seven Year War through a little shorter, with the same result as the first (in TTL) one. France receive Western Flandern (split west of Antwerp), while Austria receive Bavaria and Oberpfalz, the Wittelsbach receive Luxembourg, easten Flandern, Austrian Brabant and Berg-Jülich. Russia receive the areas of Poland they gained in the second partipations.
Saxony are force to give up the Polish throne to a Russian puppet and George III of UK are forced to give up Hanover to his younger brother William. Beside that UK are forced to recognise the independence of the North American colonies.
Years later The French revolution turn less bloody (more succes in the wars more popular King) and a made into a constitutional monarchy. Europe stay peaceful until the War of Palatine Succesion in 1799. Which the Louis of France try to use to regain popularity to reestablish Absolutism in France. The war turn into a bloody mess with French armies march through Germany, and the German Prince join behind the Emperor. After year of War a peace are reached France receive Brabant, East Flandern (except Anwerp which are given up to Netherlands) and Liege but give up Elsass. The Austria receive Sundgau, while the old states are restablish in Elsass, Pfalz are given to the Emperors (Joseph II) nephew Charles of Teschen.
The Empire are reformed and the Imperial Circles are fully reestablish in most of Germany* (through for some circles they follow the bigger state border**), more or less with the power of the later Länders. The crown are made fully heritable, but all the new Circles gain voting right in the new Parlament. Which gain control over taxation and internal customs.
*Oldenburg and Vorpommern aren't made part of any circles because of their foreign ownership.
**Schleswig-Hostein, Brandenburg, Hanover and Saxony.