I know many young BC pups that we have rescued from shelters because they were too young to be there but staff didn't care. Many wind up dieing.

Also, I disagree with sticking him on a high quality food right away. I run into a problem with my fosters when they come in and we give them Acana. They get the runs and don't stop until they are fed a slightly lower quality food.

None of my fosters have ever been able to handle high quality food.

Back on topic, though...

I would suggest Nutro. Or Pedigree (many here will disagree with me on that, though).

It's nice to know you are keeping him! That pup is so lucky he wasn't severely injured when that idiot threw him out the window.

I think you need to post some pictures of him!