The key difference is that Tuchel favours a 2 man midfield as opposed to a 3 man midfield as Sarri did - Kante has always been an awkward fit in the latter system, because his strengths simply are running more than the opposition and pressing high to win the ball whilst someone sits behind him.
Kante's best moments have always come when he's been part of a pairing - be that with Drinkwater at Leicester, Matic at Chelsea, or Pogba for France. Given that, it's encouraging that Tuchel has said Kante's best position is as a part of a double 6 - far better to use him there than to shoehorn him into a role as an 8.
I believe he played 4-4-2, 4-2-3-1 and 4-3-3 in Paris but probably primarily because he needed to adapt the system to get the best out of Mbappe and Neymar and free them up from defensive work.
In Dortmund he preferred a 4-1-4- and I think his time there represents his ideals best. As a six he favoured Weigl who's basically a light version of Busquets. Jorginho is closest to him. I could be wrong but I don't thibk Kanté fits his system particularly well.