I need an infinite canvas

As far as iPad’s memory is concerned, it’s not infinite. Hence no infinite canvas can really exist.

You can however have the canvas automatically enlarge while you draw. Here is how:

  1. Make sure your canvas size in Preferences > Canvas Size is Auto.
  2. Draw or move objects towards the right or bottom edge and the canvas will automatically enlarge, no questions asked.
  3. If you’d like to have some more space to the left or to the top, select all shapes and move them to the right or to the bottom.