This seems to be a fan-made poster.
It was made by a deviantART user called Omnipotrent. Their copy of the poster is here: http://omnipotrent.deviantart.com/art/The-Chronicles-of-Narnia-The-Silver-Chair-401179595. Quoting from the description:
I think it's safe to assume that there will not be a fourth Chronicles of Narnia installment, however if their [sic] was, I chose Jamie Campbell Bower from City of Bones to play Caspian's missing son Prince Rillian.
As such, you shouldn’t read anything into the actors portrayed in that image. (Although within a month or so of this poster being made, the 2016 movie was announced, so who knows.)
Source: I used TinEye to look up the image, and that dA page was the first result.