Kante is not a box2box midfielder as he does not have the skill sets to be one,. A box to box midfielder is a CM that contributes on both the defensive and offensive sides of the ball (essentially a 2-way player). Kante wins back the ball and makes short range passes, he rarely dribbles nor gets into the opposition box and is overall offensively challenged. He is more like Makelele than Vidal or Ramires
This is independent of where the coach decides to play him (e.g. Mourinho playing Fellaini upfront doesnt make him a striker). At Leceister, Drinkwater was the more attacking of the midfield pairing, and a better exmple of what a box2box midfielder is. At Chelsea, both Kante and Matic are DMs (one of the reasons they are difficult to breakdown) with Kante being more mobile, while when Cesc is playing along side Kante, Kante is the only DM.
Herrera on the other hand does have the skill sets of a box2box midfielder, no more clearly exemplified by his performance yesterday: man marked an attacker (which typically means you spend most of the time in your half); provided a through ball pass from midfield to setup a goal; and scored a goal himself. Last season, Herrera scored 5 goals in 27 appearances while Kante only managed 1 in 40.