I don't think it's ASB to have Rome win at Cannae. Really, you just need them to adopt a more spread out formation, rather than making it more compact than usual. Basically, have the formation spread out much wider than the Carthaginian formation in front of them. They have the numbers to do it and it doesn't take any military innovation to do it. It's hard to be encircled when you are pushing hard on the flanks as well as in the middle.
That said, we have to remember Hannibal chose this battle. He chose it knowing exactly how the Romans were planning to fight. So with that in mind, if the Romans are adopting a different strategy, Hannibal's not going to fight. He's shown in the past and in the future that he could escape virtually any attempt to pin him down, so they can't force him to fight. He's only going to fight on his terms.
So if anything, Hannibal's just going to win another ambush battle as the Roman consuls get less patient and more careless in their eagerness to win a battle against Hannibal before their term is up. More importantly, Rome will still think they can defeat Hannibal in a conventional battle, a fiction that won't be shattered yet like it was at Cannae. So in a couple years you probably have TTL's equivalent of Cannae occur. And that would actually have far worse consequences than OTL's Cannae for Rome. Rome'd likely have to abandon their campaign in Spain as well (they'll desperately need the veterans in Spain) and that frees up Hasdrubal to head to Italy much earlier than OTL.