I heard Chows have bad temperament and are fairly aggressive. Im not sure as I dont have experience with them but the more attention and effort you put in to them, the nicer they will be. Dont give up, thats the biggest mistake people make. Labs are great though. Its what I have and the only one Il ever have... maybe. lol
Good luck!
It's great you rescued a dog. I have a special fondness for those ex-street dogs. They are tough, and in my experience peculiarly grateful in almost a human way for the pleasures of a nice life.
But he has a difficult background. Abandonment, no doubt. Hunger. (he's probably got used to raiding bins for food) He will have plenty of issues. Although he might be quite well socialised. (If he was alone on the streets, he will have learned that inappropriate aggressiveness towards other dogs etc, will get him nowhere. For survival reasons he may be easier toward other dogs and/or people)...I don't know.
I have no experience of Chows however. I hope someone else posts who does...