The Austrian Habsburgs win the War of Spanish Succession. Maria Josepha of Austria remains the Habsburg heir and marries Frederick Augustus of Saxony, who eventually becomes Emperor Frederick IV as a result. Their son, Fredrick Christian, consequently inherits Austria, Saxony, Bohemia, Spain, Hungary and Poland.
Holy Roman Emperors
1745 - 1763: Frederick IV, m. Maria Josepha of Austria
1763 - 1763: Frederick V, m. Maria Antonia of Bavaria
(Following the War of Bavarian Succession, Emperor Frederick VI, whose mother was the eldest sister of the previous Elector of Bavaria, adds the electorate to the Wettin domains, becoming the sole Imperial Vicar of the Holy Roman Empire.)
1763 - 1806: Frederick VI, m. Amalie of Zweibrücken-Birkenfeld
Idk what happens following the HRE's dissolution (if it is dissolved). Napoleon and Frederick Augustus III (who is Frederick VI here) will be on less friendly terms due to the lack of a need for Frederick to restore Poland as a French client state. Does the Wettin monarchy find itself eaten on two fronts by France and Russia?
On the other hand, if the Wettins lost Poland to a partition (or partitions) by Russia and Prussia, an alliance between Napoleon and Frederick to help Frederick regain Poland that develops into long-term one might be possible. Does Napoleon stay in power then? The HRE is not dissolved. Napoleon becomes Holy Roman Emperor. He weds Frederick VI's daughter (who was unwed IOTL).
1806 - ????: Napoleon I, m. Maria Augusta of Saxony
Elector of Saxony (also Archduke of Austria, Elector of Bavaria, King of Bohemia, King of Spain, King of Poland, King of Hungary & King of Croatia)
1763 - 1827: Frederick Augustus III (formerly Emperor Frederick VI)
1827 - 1836: Anthony I
1836 - 1854: Frederick Augustus IV
1854 - 1873: John II
1873 - 1902: Albert V
1902 - 1904: George I
1904 - 1932: Frederick Augustus V
1932 - 1968: Frederick Christian II
1968 - 2012: Maria Emanuel I