A climate system in Subaru Impreza has special cooler for radiator. Buying new AC fan for 2003 Subaru Impreza you better choose original one. It has 2 poles if speaking about 2003 model year.
The best choice for 2003 Impreza is to purchase factory parts by Subaru. For Subaru cars with engine 2.0 liters you should note exactly the voltage of 12 V which is needed.