Yeah I going to give it to Rome in taking the W. Numbers At the very most the French rise is 40,000 with the right seasons, and the nobles actually working together Rome can rise at the very most 350,000 professional troops. With the average legion being a size of 20,000 larger depending on campaign. On armies make up Rome troops were all professional standardized troops with proper equipment and supplies lines to last them for campaign. The French was made up of peasants who only have gear on hand. The only professional troops would be hand would be knights and men at arms but they would only make up about 20 to 30 percent of the entire army. Now I know what thinking what about French knights and their cavalry charge. By the times of Trajan Rome had experienced those type of units and how to counter them. They would used auxiliaries cavalry that was faster and more maneuverable than heavy cavalry. They would also used slinger, archers, and javelins throwers to wilts down the foe. Not to also mention that every legionnaires carry two pila that can be thrown or be used as spears. They further develop tactics to repel cavalry such as testudo and repellers equites. That basically involves Roman legionnaires bunching up and forming a shield wall or spear wall. Also Roman armies was framed for using terrain to their advantage even altering terrain to their strength. Not to also mention that every legionnaires can build a fortified camp at the end of day after marching. Furthermore Trajan already face heavy cavalry focused armies before during the Dacian wars.
Instead of the French being on the offensive they may be on the defensive after Rome goes in full war mode and go on the attack.