I didn't think it was ever in question that Walt would do that to Brock.
Gus's plan was almost perfect except he didn't account for the fact that Jesse truly knows Walt. Gus probably assumes everyone involved in this business is capable of doing horrific acts just to get revenge. But Walt has been a family man since day one and Jesse knows that. Jesse also knows that Walt is the only father-figure he's ever had respect for.
I should have watched it again, but I thought right before Gus got to his car, he glanced at a different car in the parking lot. One that had something hanging from the mirror. My first thought was that it was Walt's car, but now I'm not so sure.
Jesse gave way too much away when he said Brock was poisoned. Gus was either expecting Jesse to say, "I don't know what's wrong with him" or "Walt poisoned Brock, and I killed him for it." When Jesse indignantly said that Brock was poisoned with no other details, I bet Gus's alarm when off. And that's why Gus ended the conversation immediately and told Jesse to not come back to work until next week.
I don't know if they kill Gus this week. I hope they do because if they don't, I bet it's going to be a big cat and mouse chase next season for the first half. If they kill him off now, the story can really open up.
I'm really sad this season's coming to an end. I feel like it just got started.