Most likely here Francis Stephen will end marrying a French princess like his father
Perhaps. Alternately, it is simply a case that he may be married off to Maria Theresia's younger sister. ICR who was the person who proposed this swap OTL when they were
earnestly considering one of the other options, but they said: Maria Theresia will marry [insert groom], and in a few years, Lorraine will marry Maria Anna. His parents wish him to marry an Austrian archduchess. They do not particularly care which one."
AFAIK, OTOH, Élisabeth Charlotte was
not in favour of the marriage of her son to Maria Theresia, since she essentially told François that the Austrians were fucking him over (which they
were), that they were leading him around by the dick (again, they were), and she said that she would wear her funeral shroud to the wedding, because it would happen over her dead body.
However, Louis XV poisoned
that well (François marrying a French girl) when he [Louis XV] refused to marry Élisabeth Charlotte's daughter. The younger Liselotte never forgave the French for doing that.