From the Construct manual:
"Set canvas size
Set the size of the canvas area in the page, if appearing inline to the page (i.e. a fullscreen mode is not used). If a fullscreen mode is in use, this effectively changes the size of the Window size project property, which adjusts the size of the viewport."
As I said before, you can't set layout size dynamically. You are mixing Layout and Viewport/Window. These are two different things. Imagine your construct app/game as something you look through an actual window:
+--------------------------------+
/ B /
/ +--------+ /
/ / A / /
/ +--------+ /
+--------------------------------+
[/code:4xmvrgdt]
B is the full Layout, A is the Window through which you see the Layout. As far as I know you can set the window size dynamically, using set canvas size, but not the layout size.