Agree with the above posts about documentation - both aircraft and pilot. They are very thorough and strict.
Another route is over to LFPN (Toussus les Nobles) or even Issy Heliport (not as expensive as Battersea and much easier to get into from the West) then down the centre of the country to LFLY Lyon Bron, very efficient and cheapish, then on to Cannes.
For Cannes, if you do not flight plan then you must do an 'Intention de vol', as Cannes is one of 7 airfields which require this (part of the military requirements - phone the local CDC - see AIC 69/03 on the French AIP website). As with the other airfields, make sure you have the VRPs along with required altitudes. At Cannes, they could send you out over the water to join from the SE.
Apart from that, take a comfy cushion.
HO
Once at Cannes, make sure you don't wander around airside, they have recently clamped down on the security and will lock you up if you do not have the correct passes.