To be certain, you should:
1. Consult your owner's manual: This is the best source of information for your specific vehicle. It will have diagrams showing the location.
2. Use a repair manual: A Haynes or Chilton repair manual for your year and model Escalade will have detailed diagrams and instructions.
3. Look online: Search for images of a "2003 Cadillac Escalade [engine size] oil pressure sending unit location." You'll likely find pictures from other owners that can help you pinpoint it.
Remember to be careful when working near hot engine parts. Allow the engine to cool completely before attempting to locate or replace the sending unit.