A very interesting possibility that I had no idea about! I mean I knew of the plans of Emperor Josef I to partition Bavaria with the Palatinate and annex the Duchy proper, but I had no idea that Maria Theresa also made a play for the Electorate as well, considering her relative disinterest in her son's attempt to claim it in the War of the Bavarian succession.
First off, the best bet would be in 1745, as realistically there's no reason for a winning Charles-Albrecht to countenance trading his homeland for the Austrian Netherlands. Actually, I think the best bet would be a POD in late 1744, when in OTL a combined Franco-Bavarian army, assisted by the Prussians, drove the Austrians out of Bavaria and enabled to Charles VII to return to Munich. That way, Charles VII instead dies exiled in Frankfurt, and Bavaria remains under Austrian control. Combine it with a TTL Battle of Pfaffenhofen that destroys what remained of the Bavarian army, and you have a desperate Maximilian III willing to try anything to salvage something from his father's mess.
Second, the question becomes which state Max would get, the Austrian Netherlands or Tuscany. Considering that MT wanted to keep everything she inherited, I imagine she'd prefer swapping Tuscany and making her husband Duke of Bavaria instead, but that might not be wise as the AN were under French occupation by this point and Louis XV would likely resist returning them if he loses his Bavarian valve to turn against Vienna. I suppose it will depend on whether or not MT thinks she can liberate the Netherlands or if she has to acquiesce to the loss. However, for the sake of the question I'll assume MT acquiesces and trades the Netherlands for Bavaria (which would have to be ruled by her husband, as legally Bavaria didn't have any kind of pragmatic succession).
Third, France. the Austrian Netherlands themselves. By making the trade, Louis XV is in a bad position. After three years of blood, sweat and tears France had at last taken full control of the southern Netherlands and seemed poised to finally annex them, only for the provinces to be sold out from under them, to their own ally no less. If he ties to hold onto the provinces in spite of their transference to the Elector, then French duplicity is exposed to Europe and Versailles becomes an untrustworthy ally that steals territory from her friends. yet if he acquiesces then France has wasted tens of thousands of lives, millions of livres and three years for nothing. However, on the other hand, he's still in a better position than OTL. Instead of returning the Netherlands to Austria for 'honor', the King instead hands it over to a trusted ally. And the French people are likely to blame that perfidious Queen of Hungary for her duplicity rather than their beloved King, whose honoring his trusted fallen ally. Plus it means that, for the first time in nearly two and a half-centuries, the southern Netherlands are permanently in the hands of a trusted ally of France. Not the best case scenario, but still pretty good.
Finally, the Austrian Netherlands themselves. In all honesty, its a sucky trade for the poor Elector. While the Austrian Netherlands were nominally very rich, strategically important and a major crossroads in European trade, in practice none of that was still true. Instead of a central legislature, a central tax collection agency and a unified law code the Netherlands were a personal union of ten provinces, each jealously guarding their rights, privileges and powers. Getting money out of the various estates was like getting blood from a stone. Then there's the fact that the lifeblood of the Flemish traders, the Scheldt river, had long been closed by the Dutch, who controlled its mouth. The great port of Antwerp withered on the vine, as did most of the customs duties for the provinces. Finally, they even lacked control of their major fortresses, as the strategic fortresses of Veurne, Knokke, Ypres, Menen, Dendermonde, Tournai, Mons and Namur were all garrisoned by the Dutch. So the Elector would have a very uphill battle to create a centralized modern state out of his new realm. As for his title, it would be Duke of Brabant, like the last independent rulers in Brussels, the Archdukes. The provinces were still part of the Empire, so no royal title would be allowed, and each were in a personal union, so the Elector couldn't really annex them into a new state.
Hope this helps.