The Giver is told in the third person, but focuses exclusively on Jonas. We know what he's thinking and feeling, and we don't enter into anyone else's head. The narrative often just goes into telling mode, giving us the background info we need about the way things work in the community, but just as often we get the info in a contrived, "Jonas is thinking about this" sort of way.
So it's not the most elegant device in the world, but it gets the job done. As far as Jonas being our protagonist, this is a great choice of narrative voice, since it really gets the reader invested in the novel's hero.