As all strikes, this will start out tough. There are many sources of information and links that have been given in past posts.
For April 3rd it is estimated that one TGV in 8 will run. 20% to 30% of RER B from Gare du Nord will run
This link includes estimates for Thalys and the Eurostar
Air France has announced further strikes on April 10 and 11.
Edited to include Deutsche Bahn info