Francis of Lorraine not the Grand Duke

The Grand Duchy of Tuscany was a central Italian monarchy. Tuscany was ruled by the House of Medici.
Gian Gastone de'Medici was the last Medician Grand Duke of Tuscany. He reigned 1732 to 1737.
Tuscany was transferred to Francis, Duke of Lorraine and husband of Empress Maria Theresa of Austria.

Suppose the Grand Duchy of Tuscany does not go to Francis of Lorraine.
Who shall be the Grand Duke of Tuscany?
 
I have been wondering how things would have turned out with a savvier Charles VI.

With Britain being such a bad ally (disband the Ostend Co. in return for no assistance), what if he pursued a detente with the Bourbons?

Treaty of Nice (1730):

Austrian non-interference in Poland
Lorraine to Stanislaw is he loses in Poland, to France if he wins
Guarantee to Austria re: Naples and Sicily
Charles of Bourbon to inherit Tuscany
Marriage of Francis Stephen, Duke of Lorraine to Maria Theresa. The two will be co-rulers of Naples and Sicily.

Stanislaw loses in Poland and the treaty provisions kick in. Charles becomes Grand Duke of Tuscany in 1737. Naples and Sicily become the Habsburg secundogeniture that Tuscany would have been.
 
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