Before her marriage with Charles II of England and Scotland the Portuguese princess Catherine of Braganza was a candidate to marry Louis XIV of France. At that time both France and Portugal were at war against Spain. However, the Treaty of the Pyrenees was signed in 1659, ending the Franco-Spanish war and arranging the marriage of Louis XIV and Maria Theresia of Spain.
But WI Catherine had been married to Louis XIV before the peace were done, of the war had lasted a little longer and the marriage had been done? Now is Louis XIV who would probably suffer the fate of Charles II and never have children (it would have interesting consequences when the Spanish Habsburgs die out). Also, who could be married to Charles II, and maybe continue the rule of the House of Stuart? And who would probably marry Maria Theresia, replacing the Bourbons as the probable line of succession for the Spanish throne?