No, there's no option to improve the quality of the display.
There are only video mode (576, 480, progressive or interlace, widescreen or not).
Is your problem only on WiiU ? did you try on a Wii ? Maybe the problem is due to the way the console does the oversampling resizing over hdmi?
Your TV is probably not 720p, so if it's bigger there's a process to make the image bigger to fit your screen.
Maybe try to go to WiiU settings and set a lower resolution so there won't be process done by the console but only by your tv?
Also, games usually look better when it's not using widescreen mode, but user rarely like 4:3 pictures on a wide tv.
Or maybe, you know, that's just how that game looks.