Romans lost the battle of Cannae because they were too dedicated to their miliary doctrine. Untl they faced Hannibal this doctrine won them lots of battles and they saw no reason to change it. After such a great defeat when every odds were in their favor, the understood that they need to reshape their doctrine their way of waging war. And when they did, with a great commander such as Scipio Africanus they defeated Hannibal.

Tend to agree with Pars. All other things being equal, Caesar would have lost at Cannae. What Caesar might have done was engaged Hannibal on more favorable terms.

The Romans of 216 BC were very amateurish at war. They had been very successful in the past but they had not seen serious war since 241 BC and that war for Sicily was won at sea as it was stalemated on land.

 

The Rome of Julius Caesar's time had seen a considerable amount of very serious warfare. There had been civil warfare between Roman armies and wars of conquest of non-Roman peoples such as the Gauls.

 

Marcus Crassus had lost to the Parthians but the account of this by Plutarch attributes to Crassus a great deal of over confidence combined with unpreparedness. That may be why Crassus' army reacted threateningly to Crassus when he at first refused to go away with the Parthian party sent to take him prisoner.

 

The success of Hannibal at Cannae is probably attributable to the naivete of the two Roman commanders, over confidence based on their great numerical superiority and according to Polybius Hannibal's relative balance between infantry and cavalry. In the battle, the Roman army was boxed in cleverly and butchered methodically. Something like 70,000 died.

 

It is very hard to believe that all but the most incompetent generals of Caesar's Rome would not have avoided Hannibal's trap and instead would have offered battle under more advantageous circumstances. Caesar, Marius and Pompey each would have beaten Hannibal in war, I believe.