One thing about the pitbull breed is that it isn't a 'pure breed' at all. It's a mixture of over 15 bully breeds, and yes, that includes the boxer as well as other pit breeds like staffordshires and american pits, etc. You're guy could possibly be a pitbull breed, but will boxer as the primary breed. Never know unless you do the genetic tests. Even then, you may get a complete mix of primary, secondary and minimal mixes which won't specify a certain main breed anyways.
Your guy could be a boxer, just a poorly bred one. Could also be some other breed in the mix generations back. My staffy looked all pit when I got her. Once I studied up on the breed, I understood how the confusion comes about. She was a staffordshire as her primary breed, but somewhere in her lineage, there was a cavalier. The cavalier only showed in her demeanor and the way she ran. Other than that, she was all staffy.
In short, your guy can be whatever you think him to be. Until he is about 2, he will be changing quite a bit. Being all white, it's tough to see the breed without the markings. To be safe in a questionable neighborhood, I would continue to say he's boxer.......and if or when you do the genetic testing........saying boxer mix is perfectly ok!!!
LISA ~ Lily LaRue - 4/07 boxer; Buster McDoogle - adptd 6/07 Vizsla/Besenji mix; Annabella Kanicki - 5/08-7/09 staffy; Mr. Smiley - 4/10 Boxer/pibble mix; Fozzy Bear - 5/10 Red Heeler/pibble mix