How to implement a background that will stretch?

Question

Unity

This situation has developed, I'm making a game in the TD genre. Everything would be fine, but I ran into a problem. The background that I have I can perfectly fit only one device, while on others the screen will be wider somewhere, somewhere narrower. And accordingly everything will change. But in this game this cannot be allowed, here the important point is the presence of roads, they should occupy not only the square in the center, but bend along the entire screen and, accordingly, the idea of ​​drawing too much so that it is cut off does not fit.
How to be in this situation? I wanted to ask if it is possible to make a canvas under all other UI Elements, as well as 2d sprites that are on the stage? I could stretch it out and use it, or any other ideas?