If Louis, the dauphin (son of Louis XV) did not marry Maria Teresa Rafaela of Spain in 1744 who else could he have married?
The double Spanish marriage was to patch things up after the breaking of Louis XV's engagement to the OTL queen of Portugal.
Now, most of the candidates listed here were considered after Maria Teresa's death, but age aside, they'd probably fit:
• Maria Antonia or Maria Anna of Bavaria, daughters of Emperor Karl VII
• Maria I of Portugal or one of her sisters - her mom blocked any talk of a French match OTL. Probably will here too.
• Maria Anna, Maria Josefa or Maria Christine of Saxony, daughters of Augustus II of Poland
• Eleonora Maria Teresa, Maria Luisa or Maria Felicita of Savoy
• Maria Teresa, Matilda or Fortunata Maria d'Este, their mom was in France and a French princess, so I could see her lobbying for one of her daughters as dauphine
• Elisabeth of Baden-Baden, only surviving child of Ludwig Georg (who originally wanted to marry Marie Lesczynska). It's not clear her dad won't have sons/nephews yet, and the match between her and a Durlach cousin (Christoph August, I think) was only considered in the 1750s
• Auguste Elisabeth of Württemberg. Originally her brother wanted her to marry either the dauphin or the duc d'Orléans but struggled to get the money for a dowry.
• Elisabeth Auguste, Maria Anna and Maria Franziska of Pfalz-Sulzbach. However their grandfather hoped for a grand Wittelsbach union between his three granddaughters, and the three heirs to the Wittelsbach realms (Karl Theodor in the Palatinate, Maximilian III in Bavaria and Friedrich Michael of Zweibrucken) - honestly the last girl, Maria Franziska seems most likely to be dauphine.
• Therese Natalia of Brunswick-Wolfenbuttel. Originally considered for dauphine, and suggested by Friedrich the Great, but the French were leery of a match with a Protestant princess, even though Fritz assured them a conversion would be no problem.