Your mockup imposes limitations, mainly having to do with canvas (or also window sizes)
This only applies to mobile, and I think you said you were developing for mobile (correct me if I'm wrong)
The limitations:
Your picture implies (if I'm correct) that you also want the canvas to change in size, but if you're on a mobile device, this is not a good idea, generally speaking. You can change the canvas size in System (and therefore, the window size), but with mobile devices, this is a bad idea.
It has to do with one, phone resolution (varies between model/brands) and two, while the following is a general guideline: there is a widthxheight limit defined as a 'safezone', this describes if as long as said limit is not surpassed, a game will display fine on almost any mobile device.