http://heliosinteractive.com/scaling-ui-hololens/ 

https://forum.unity3d.com/threads/unity-ui-on-the-hololens.394629/

1.Create a World Space Canvas attached to the Camera (or using a Tagalong, etc)
2.Set its width to 126.8 and its height to 72 (mirroring the 1268×720 resolution)
3.Set the Dynamic Pixels Per Unit to 10 on the Canvas Scaler
?4.Magic Time?: to make the canvas the full size of the viewable area, set its scale to its z-distance from the camera * 0.00415f.

Unity UI on hololens