Usually nice dress pants/chinos and a collared shirt are the way to go. Make sure your shoes match your belt (which you will be wearing).
Wear a sportsjacket if you like but it's not like some snooty French guy is going to be like "excuse me sir...".
No sports attire
Avoid cargo pants
Basically you don't need to get that dressed up, but you want to avoid looking like a slob.