The XTS does not come standard with navigation in the base model, and it cannot be optioned. The company would have had to elect to purchase a XTS Luxury (navigation is standard in a Luxury edition), so in the end whether it is part of the fleet will be very dependent on the vehicle actually rented at that time. Enterprise Holdings in my experience doesn't generally opt to equip vehicles as well as some of the other brands/companies, however in looking at fleet vehicles Enterprise is selling of the Cadillac XTS, all of them are actually Luxury editions, so they have factory Navigation.

Also, note, you reserved a Luxury car, which offers as an example, the Cadillac XTS, but it could be a different car altogether.