Took my 2006 Megane II (2006) CC in for an auto gearbox repair, when collected the bonnet release handle inside the car was functioning but there was no resistance to the cable and obviously not popping the bonnet. Took car to Renault dealership - they had never experienced this before and stated it would be a half day job at least to put right. At their prices I decided to have a go myself - Haynes manual to locate the bonnet mechanism and cable connection positions and then I started.
There are two cables that operate the bonnet release - from the handle inside the car this one terminates about level with the nearside headlamp/battery position and has a nipple connector. The bonnet release mechanism cable is about 2 feet long and has a cup shaped end to it that accepts the nipple end of the other cable. Both ends are housed in a plastic box attached to the slam panel directly opposite the battery. Inside this box the two cables connect to each other. What happened in my case was the short bonnet release cable had been pushed downward when the mechanics were working on the car - this separated the two halves of the plastic box and disconnected the cable joint. It is extremely easy to do this and I recommend all owners undertake a similar preventative measure that I explain later.
To get to this cable there are two methods - raise the front of the vehicle, remove all the under side plastic trays and access the cable by reaching up into the engine bay - the second method which I used was to remove the nearside front black plastic grill by the headlamp - get your fingers under the bottom edge starting at the headlamp and pull upward, the plastic grill separates from the bumper and as you move along it's length it will release without damage. Get a good torch and shine it in - you will see a grey plastic grill up top of the radiator by the bonnet - pull that free, mine came away with minimal damage and I can't actually see what function it served anyway. Reach your hand palm up between the top of the rad and the bonnet and move backward into the recess until your fingers feel the plastic cable sleeve which runs underneath the slam panel. Get a grip of this and start to free it downward as you also pull it back towards you - it should release easily and the U shaped cup end of this cable will appear - pull this cup and the bonnet opens. - From inside the engine compartment reconnect the two cables carefully reassembling the plastic box that houses that connection - I then drilled two holes alongside the box and using cable ties I ensured the box will not inadvertently come apart again. Hope this helps some one else - I do have photographs but the site won't let me post them for some reason - I don't have a security token??
Took my Renault Megane to the dealership and they were quite pricey. Don't know what
additional costs there would have been after they managed to open the bonnet in order to fix whatever they deemed wrong. I followed your instructions and to my delight I opened the bonnet. I also reassembled it using your cable tie idea.