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.
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)