Internet provider subscription from abroad
We want to have a box active when we get to Paris with mobile # we can use prior to moving.
To get an Internet plan, you need a French RIB (bank account) and a proof of address in France (not just an address France but proof that you live there like an electricity bill). That's why I don't think you can get an internet plan from abroad.
I'm afraid you'll have to go with data SIM cards or eSIM.