This post provides instructions how to resize canvas in Google Draw.
For general canvas resizing, look to the bottom right corner of drawing for the “grippy bars.”
Click and drag this corner will resize the canvas.
Warning: immediately after resizing the document adjusts the zoom so that it appears that nothing has been changed when really the size of the image is smaller.
Use the View menu to readjust the zoom on the drawing.
For a more specific resizing use the File Menu and choose Page Settings.
Page setup allows you to set the canvas size, including a custom size.
Enter in the number of inches or pixels you want your drawing to be. Try out the Ruul chrome extension to help you determine what size you need your canvas to be.
Custom Sized Canvas in Google Draw (Nov 4, 2013)