The war begins, like OTL, on the us Frontier. Prussia, deciding war is imminent, decides to strike first at Saxony and then Austria as per. This catches everyone by surprise, including their allies(it did OTL). The French begin their mobilization. Their primary and only enemy in their mind is Britain, everything else is a sideshow. However, Britain's King is also Hanover's elector, and Hannver is the one big, valuable and vulnerable target for the French army that the British navy can do nothing about. At the same time, France calls up her allies in the Palatine and Wurtemberg, who's armies begin mustering. Like France, neither is ready to act before 1757, but will form a counterweight to the rump Reichsarmee and the Bavarians. 1757 goes initially much like I have already written. Once Hanover is down, the French are free to turn back to the Austrian Netherlands, if they feel like it. But the Austrian Netherlands have very little to no offensive power, and not much ability to resist. If the French choose, it will be a replay of Saxe's campaigns of 46-48. But honestly, with Hanover down and the Rheinland secure, there isn't much reason to. The French do not want to antagonize the Dutch, and the Dutch(having learned from the War of Austrian Succession), do not see any benefit to joining to prop up the Austrians. Prehaps the French can temp the Dutch with pieces of the Austrian netherlands, I'm not sure how wedded the Dutch were to neutrality, but I suspect fairly strongly. They are surround on all sided by enemy or enemy held territory, and the British navy off their shores.
After winter the Prussian invasion of Bohemia goes per OTL intially, with the defeat at Kolin causing him to pull back and regroup.
July of 1757 things start to diverge more. The second French Army, under Soubise, crosses the Rhein and links up with their allies, to face the rump Reichsarmy. The French army alone numbers 24,000, with her allies and auxilliaries it will be over 40,000(Palatine and Wurttembergers). Facing her is the Reichsarmee, (OTL Paper strength of 50,000, but never had more than 25,000 thousand in the field OTL, and that was with the Palatine and Wurtemberg contingents, who are not there), plus 8,000 additional Austrian troops. The French defeat the Reichsarmee, and Saxony is more secure then ever.
Frederick is please by this(OTL this caused him to pull out of Silesia, because those two armies joined up to invade Saxony). He is able to depose his troops as wishes, and wait for the Austrians.
The Austrians are now faced with a tough choice. Divert more troops to Bavaria and the Reichsarmee, or keep your forces against Frederick. It doesn't really matter. The troops Austria had OTL would win again Bevern at Breslau, without Frederick there. TTL, this does not happen.
And this is where it gets pretty detailed, if you want specifics, you'll have to look them up. Sometime in late August or early September, Frederick will be able to bring the Austrians to battle(he does not leave to Saxony on Aug25 per OTL). Frederick will get his Leuthen, but on a grander scale(it will not be 28,000 Prussians vs 70,000 per OTL, with 6,500 Austrian killed and wounded, and about 21,500 Austrians were taken prisoners the day of the battle and during the following days. The Prussians captured 51 flags and 116 guns. The Prussians lost in killed 1,141, in wounded 5,118 ) TTL it will be 56,000 Prussians(the force Frederick had before spliting it in the face of the Saxon invasion, against 95,000 Austrians(Nasdady force will still be there, and will not have gone to Moys, Winterfeldt will not die). So for easy of numbers, we can roughly double the outcomes(but I will be lenient on Austrian prisoner numbers). Call it 3,000 Prussians killed, 10,000 wounded, to 13,000 killed and wounded Austrians and 35,000 prisoners. Austria has lost half of her entire bohemian forces, and Prague is now wide open to Frederick.
Frederick will take Prague, going into winter quarters there and gather additional funds and troops in Bohemia, clearing out any remenant forces in the fall.
I suspect at this point diplomacy takes over. Maria Theresa has always been willing to cut a seperate deal, and over the winter some agreement will be reached. Prussia will get the rest of Austrian Silesia, and Saxony, and peace out of the war, leaving France holding Hanover and staring at Britain across the channel.