You are very good in keeping the suspense!The Winter Maneuvers
"...what I would give to show our friends in Russia that we mean them no ill-will, no offense, and only courtesy..."
- Eugene de Beauharnais
The German war scare only intensified into the winter of 1813 - suggesting a probable Fifth Coalition being formed to challenge French supremacy in Germany by the following spring by, at the least, Austria, Britain and Prussia with the possibility of some of the Confederation's statelets throwing their lot in with them. With the armies of Italy, Spain and the Netherlands, in addition to most of Germany and the experienced French armies, Napoleon felt good about his odds in such a conflict; he would quite possibly have his most robust advantages in any coalition yet, even with the army reforms pursued by Vienna since Austerlitz. This, of course, was provided that Russia was not led into war by the nose by her Prussian ally, and a number of French statesmen winced at the thought of Napoleon continuing the fickle and fragile dance of diplomacy to keep Tsar Alexander out.
Eugene de Beauharnais met with Alexander's envoys personally at Regensburg in late November as rumors spread that von Dalberg would retire entirely on his 70th birthday - the following February. Eugene assured Alexander's men as well as the Duke of Oldenburg that as prince-primate he would suborn no royal or ducal rights in any kingdom and that his sole goal was to pursue a uniform foreign policy for the Confederation to keep peace in central Europe. The Russians, of course, were skeptical; but the "Regensburg Reassurances" seemed to have done their job in convincing them that under the soon-to-be "Prince Eugen," a more fully-federated Germany was not a risk. The ongoing diplomatic antics of Joachim Murat in Berg further satisfied Russian worries of a future unified, singular Germany being a creature of Paris; Napoleon, after all, could not even get his brother and brother-in-law to cooperate, so why would they listen to his adopted son?
Prussia and Austria, meanwhile, had their own work to do, planning a joint offensive into Saxony and Warsaw to start off the coming war while Austria, with British support, launched an attack into the Kingdom of Italy. Contrary to prior conflicts, both states agreed - contra British intentions - to keep their war aims limited. The goal of this Fifth Coalition would be to dissolve the Confederation as a buffer state and undo some of the imposed territorial humiliations of the previous wars; beyond that, both Austria and Prussia accepted that there could be no dislodging of Napoleon at all, but with the tide of revolutionary governments seeming to have mostly receded (Napoleon's firm Spanish ally was perhaps one of the most conservative regimes on the continent) the ideological underpinnings of the Coalitions had waned. Only Britain still really aimed for a Bourbon Restoration in France, and they had their hands more than occupied with their Spanish-American ulcer.
Napoleon mobilized 100,000 of his soldiers after Christmas and began maneuvering them to winter camps on the Rhine so that he could launch an offensive as soon as spring began and catch his enemies off guard; in a meeting with South German kings and their generals in Stuttgart in early January, he described his strategy as having their soldiers put pressure on Austria via Salzburg, while he routed his soldiers straight through the Fulda Gap on a lightning march into Saxony, which was already steeling itself for the spring war, to crush the Prussian and Austrian forces separately before they could link up. A joint Dutch-Westphalian force, meanwhile, would attack Mecklenburg and into northern Prussia to open up another theater. It was a gamble, and a risky one, but Ney and Massena were mobilizing reserve armies behind him as they spoke, as well as a Spanish force preparing itself. The advantage clearly belonged with the French - but again, the fate of the continent depended on how satisfied Russia was with their Baltic League and whether they would join this proposed "Holy Alliance" of conservatism, which they had resisted in previous coalitions.
The Prussians and Austrians had their own troubles to worry about as the new years arrived; late in the winter, a typhus epidemic emerged and struck the East of Europe hard. Thousands of men who would have served in the armies of the Fifth Coalition perished; thousands more in neutral Russia, particularly St. Petersburg, which was hit perhaps the hardest. Nobleman and serf died alike, including perhaps the most important of all - Tsar Alexander I, perishing after weeks bedridden, on January 30, 1814... 
 Credit to @alexmilman for this idea!
So, if I understand you correctly, the Allies are not looking for the Italian theater or just consider it a remote second with a minimal allocation of the Austrian troops. But Nappy does not have to cooperate with them and in Italy he has Bernadotte who is much better in raising the armies than Ney and Massena (BTW, I’m not sure why did you assigned them a role to which they were demonstrably ill-suited: none of them demonstrated any administrative capacities but both had been very good subordinated field commanders and, unlike OTL circa 1813 Nappy, has suitable figures, like Soult and Jourdan in his disposal ; well, it is your war to win ).
Anyway, thanks for getting rid of AI but didn’t I propose a cholera (simply don’t remember): at his accession he promised to rule as his grandmother (aka, very badly) so it would be symbolic for him to die the same way, aka in a restroom.
This leaves Russia with Constantine I who does not like a war in general (*), is scared of Napoleon (was one of the main advocates for making peace with hm) and with a high probability is going to turn Russia into such a 3 ring circus that nobody is going to pay attention to what is going abroad. His father’s march on India may start looking as an example of an extreme sanity and rationality. I’m not saying that he is going to repeat it, just that his antics were unpredictable except for one area: the insane drill of post-1814 Alexander’s reign (“acrobatics” as Paskevich described it) would look like a kindergarten play in a sandbox (**). Which, taking into an account the family history, may result in an (un)timely death from some of the Russian deadly diseases (hemorrhoids and stroke were already tried so how about a fit of sneezing or a sore throat? ).
Of course, there is also a distinct possibility of him going to war …. with Austria (let Russia down at Austerlitz) and Prussia (their war with Napoleon implies disloyalty to the Baltic League or if this us not enough, just because). He was not fully averse to a military glory and in Suvorov’s Italian/Swiss campaign was performing reasonably well. Hitting Napoleon’s enemies in a back seems to be a low risk glorious war.
(*) It distracts soldier from a parade ground exercises.
(**) IIRC, Lev Tolstoy wrote that the Guards (whom Constantine commanded) marched in a paradeground step all the way from Russia to Austerlitz.