Editor Page Canvas
The Page Canvas area gets used to build your application when working inside the Editor.
The Page Canvas is a WYSIWYG editor, meaning you can see how your app will look as you build it. To build your user interface, you can drag and drop components onto the Page Canvas.
Layouts and Views
Most often, when developing an App in App Builder, your Pages will be built using a combination of Layouts and Views.
A Layout is a reusable container you can use to arrange components on the Page Canvas. App Builder ships with a few different Layout components, such as the Authenticated and Empty. You can also create custom Layouts.
Layouts are not Page-specific and get selected on a page-by-page basis in the Page settings.
A View is all components added to a specific page rendered within the Layout. This means that when editing a Page, you're adding components to a View. Meanwhile, when editing a Layout, you're adding components to the Layout that will be available on all Pages using that Layout.
All this said Layouts and Views are always displayed and updated through the Page Canvas.
You can find more information about Layouts and Views in the Components in their docs page (Coming soon...)