Jason -

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

Mike

**edit**

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. 

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.

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.

It is there because of scroll container height.

You can add following in themesources > atlas_core > web > main.scss  to get rid of it or in your custom-style file.

@import '../../atlas_core/web/variables';
.mx-scrollcontainer-middle {
    .mx-scrollcontainer-wrapper {
        height: calc(100vh - #{$topbar-minimalheight})!important;
    }
}