Salut, Julien,
When I have faced that choice, bike shops have recommended the slightly smaller tube--in your case, the 1,95". This is because the tube will easily stretch a little bit to fit your 2" tires.
The argument is that the larger tube may fold and crease if squeezed into a smaller tire.
That said, the difference between a 2,12" tube and a 2" tire is not very great.
And, I once fitted a 26 x 1.75" tube into my Schwalbe 26 x 1.6 tires, and it ran fine for several hundred kilometres.
Hope that's helpful -- good luck & safe journeys,
John
