We so very rarely here that tone from you, Antoncho.
As Antoncho says, ferric nitrate is the known method here. I bet cupric acetate with ammonium nitrate oxidation would work as well without overoxidation. It is a very gentle reducing agent.
KMnO4 will very likely yield the carboxylic acid. I don't know how H2O2 would fare at all, personally. I myself would stick with ferric nitrate since it has been documented here.
Reduction of the acid ester with LAH to the alcohol, then oxidation to the aldehyde, is not worth all the effort just for some piperonal. LAH is damn expensive, and should be saved for more important steps, i.e.reduction of nitrostyrenes etc.
PrimoPyro