Draw Rectangles on a Canvas?

So far I've used OnGui() to draw Rectangles on the screen. Unfortunately, they aren't visible in VR, so I have to render them on a 3D Object.
How can I draw Rectangles on a Canvas instead? Is there a similar function to GUI.Box()? Or does anyone know if I can render my GUI content on a texture and paste it on a canvas?

 

Check out the Unity UI Extensions project, tons of Primitives drawing controls there for either using primitives like square, circle, etc. And even a line drawer to draw whatever you like.
http://bit.ly/unityuiextensions