Post here any analysis you have on other moves he may make, like 5. a3.
To 5. a3, doesn't the main line mean 5. .. Bxc3 6. bxc3 for various reasons? Some of which mean that retreating the bishop means giving him both temo and a stronger and more flexible pawn structure?
yes, a3 is will be responded to with Bxc3 most likely. I don't see any other novel approach that's better.
Post here any analysis you have on other moves he may make, like 5. a3.