The Canvas is infinite in size; you can scroll as far as you want vertically or horizontally, so you have complete freedom on how you set up your drawing area.

If you’d like to define a fixed frame for your Canvas, go to Settings and adjust the Page Size.

You can view the Canvas with Grid Helper turned on, and you will know exactly how to arrange your design layout, or you can set on Auto Height so that the Canvas height will cover your bottom-most element.

You can set these modes under Settings → Overall Project.