Presuming it will soon have VAG's cash, to spend on motorsport. The ideal racing series for each brand would be.

Maserati in WEC's GTE Pro.

Lanica in WRC.

Ferrari remains in F1.


Alfa in WTCC and DTM with future Giulia.

Jeep in Dakar


Anything else ?

Edit: Or maybe Maserati in LMP1 to let the Viper in GTE Pro.