A little confused, first part you say show website directly on Image target, second part you say redirected.  If you just want to open the browser, then hook into ontargetfound then use unity's Application.openurl.  if you want to show a picture of the website in 3d space, then it's a bit complicated, this should help: https://stackoverflow.com/questions/46479953/render-website-as-texture-in-unity3d-on-android