How handle get element in canvas

I would like to see an example of code that can perform a simple click action on an element in Canvas. For example: I have a canvas area of 600x800 on a web page, and it is displaying a popup. Can someone please post actual code that will give an example of clicking on the checkbox.
So far, the only “element” i am able to reference is the canvas board itself , but nothing inside the canvas board.

I have code like this:
WebUI.clickAtOffset(findTestObject(‘Back Office/Canvas’), 872, 256)

The coordinates of my checkbox (inside the canvas) are correct, but i cannot really “click” on it, because i can’t reference the checkbox itself.
How can i do this? Is it even possible?
A code example would really help, and then i can experiment with it myself. Thanks in advance.