IMO Cody has big advantages in 2 situations: corner, and certain hard knockdowns.
In the corner, Cody’s jabs will actually stuff EX Rainbow Ball (first one whiffs, second hits), so to escape you have to try to do something like st.lp xx EX Rainbow, and this might also be punishable but I’m not sure.
On mid-screen after a hard knockdown, Cody’s Double Zonk safe-jump OS works vs Blanka. Basically he does a safe-jump (depending on the situation it might only be safe if it’s an empty jump) and then you have to guess between block or tech throw because he will either do jumping attack -> EX Zonk, or jumping attack -> throw (or cr.lk xx EX Zonk, or empty jump EX Zonk, or empty jump throw etc etc). Backdash is beaten by OS regular zonk, and everything else besides blocking is beaten by the EX Zonk follow up (you can’t jump if he uses j.hk, but teching super late after this will block the EX Zonk cos the frame trap gap is considerably smaller). You can coward crouch but I’m pretty sure Cody recovers much faster than you do. I don’t remember if EX Rainbow works. I know some characters can block the EX Zonk by focus dashing into the jumping attack, but I don’t think Blanka’s dash is fast enough, and it’s a huge risk in any case. If he doesn’t go for either EX Zonk or Throw and you happen to eat eat a frame trap combo stun is practically guaranted if his next mixup lands.
Also hori balls are punishable on hit with U2 (but strangely only situationally punishable on block from certain ranges).
However, Blanka has a significant advantage IMO in the neutral game. Cody can’t quite keep up with him in footsies and eventually he resorts to focus fishing which is avoided with jab xx hop. Also Cody sucks on wakeup. So as long as he doesn’t into a bad knockdown situation and keeps away from the corner, Blanka wins the match IMO.