Is there some decentralized anti-censorship technology that can prevent this type of action, where ISPs and DNS providers and other points of centralization are forced to implement things on behalf of other parties (like Canal+ or a government)?
1. Recursively lookup DNS, so domains will have to be blocked at the registrar level, since DNS is unencrypted, it can be blocked at ISP level as well.
2. Use a protocol alternative to DNS, a good mature example is GNS. It aims to replace DNS, with a built from group up, modernish protocol. Using a DHT and public-key cryptography.
3. There are "block chain" solutions to the whole domain problem, look at Handshake, ENS etc.
No matter how decentralized something is, ultimately you need to have a server and cables connecting it to the internet located somewhere. That somewhere will be within some legal entity or sovereign's jurisdiction which you must answer to and comply with.
If whatever technology that is being used is so intertwined into the base of all use cases (including totally legal) and legal vs. illegal is practically indistinguishable at scale, then decentralization cannot be blocked without physically blocking all the legal use cases too: sure they can "cut cables" but it will have much more greater consequences as they have just cut cables connecting all the legal activity too.
DNS can be used for both legal and illegal purposes, and the French courts authorized dropping nukes on them to stop illegal activities with no damns given to the legal because the laws cited provided no such safeguards or reservations.
If you just want to prevent other central authorities (e.g. France) from barging in on the existing central authorities your computer expects to get answers from (e.g. ICANN, Verisign etc) there are plenty of projects for semiuncensoring DNS in a distributed way. But nobody is stopping, say, the US from doing to ICANN or Verisign what France is doing to CloudFlare and Google.
That's literally what blockchain solves. ENS (Ethereum Naming Service) already does this.
Other people have even argued that blockchains are states - as in governments, not as in distributed state replication protocols.