If anyone plays deeper out of the two strikers. I'd argue it should probably be Janssen. Saying that, I wouldn't play them both.
From what i've seen of him Jansen seems much more adept at holding the ball up with his back to goal than Kane. It seems to 'stick' more, this type of skill is vital at the top level. So I'd stick with Kane coming deeper. We need to give Jansen a chance to bed in before making judgements. i'm sure he'll score a hat full.