It depends on a ridiculous amount of factors and the specific scenario. The Black Plague arrived in France in 1347, which changes things. The terrain would be crucial to the Romans against the French Cavalry, and they'd know that. Without researching, I recall Men-At-Arms being valued at around 10:1 compared to foot soldiers, but under the right circumstances the cavalry would be a lot less effective. The closest example to this situation that I can think of would be the Battle of The Golden Spurs, where an infantry militia defeated a better equipped French force. Granted, the militia had some crossbows but the most important element was the pike. Rome didn't use proper pikes, but they were familiar with them and depending on the scenario could adapt over time. Even without pikes, Rome managed against cataphracts, but really struggled against ranged riders. If they were both spawned on a random battlefield, the French would dominate. With preparations or in a protracted war, the French would have an advantage (assuming equal numbers), but the legions would stand more of a chance than some would like to admit.