Keïta's similar to Can, in the sense that they are both box-to-box midfielders with high workrates - however, I don't think there's any question that Keïta is the superior player.
Keïta's attacking threat comes primarily through his vision, and his most valuable trait in midfield moving forward is his ability to draw defenders to him before finding a teammate - whereas Can makes a habit of drawing pressure and outmuscling his opposition to hold the ball before finding a teammate.
Defensively, Keïta was second among midfielders in Bundesliga in interceptions/90 and third in blocks/90 (>2k min played), so I would expect him to have better positioning / awareness than Can (who sometimes gets caught upfield). On the attacking side, he is superior to Can of last season in terms of output, key passes, dribbles, etc:
I've seen him play maybe 3-4 times total, so would definitely invite a more avid Bundesliga follower to call BS