canvas width and height control how big the page display is in the Modeler only - i.e. at design time. See documentation here: https://docs.mendix.com/refguide/page
Looks to me like the height on the scroll container is what was creating the scrollbar on an empty page. Scroll containers are typically used in layouts - I'm not sure, but it looks like the scroll container on the layout you were using has a hardcoded height, or the height is set in your theme.
I've had a similar issue in the past and fixed this by adding overflow: hidden; to the container or widget causing the extra scroll bar to appear.
there is also, whcih i have no idea what it does :D
ok i figured it has something to do with layout i was using, deleted it. still not sure what it was though.