Create a Canvas and Buttons via script - JS

Hi guys, I have been reading the forums but i did not find a direct answer for my problem:

I need to create a situation with multiple canvas on the screen and inside of each canvas I would need to create text and buttons. So what I wanted to know is how to create these via script only.

Before I used the OnGui() function but now how do I do it? And how do I create the canvas, text and buttons?

Thanks!