I am looking for surveys or any other kind of data source indicating the percentage of Frenchmen who are in favor of allowing UberPOP in France.
You can do sentiment analysis on social media feeds, but I suspect there is an inherent overlap (bias) between social media users (e.g. Twitter) and people who are pro-Uber.
To do so with Twitter, you can use the API to search terms related to Uber with the following constraints: + located in France (bounding box) + tweet text in the French language
In addition to Search, you can measure an endorsement of a view by retweets.
It's not scientific, but if you wanted to make it scientific, you'd have to hit the streets and phone lines and start very randomly sampling people.