Click the following link for an updated answer to this question: Android: Transferring images from one device to another. And, please check out the new SketchBook Knowledgebase.
Autodesk SketchBook v3.0 is entirely a new app. All your previous canvas files should be found in the Gallery with your other SketchBook Pro or SketchBook Mobile v2.x app.
Your current version of SketchBook has not been updated. It will remain on your device until you remove it and can be downloaded at anytime via the Purchase or My Apps tab from iOS App store or Google Play store. Click here for more details for downloading your past purchases.
If you open the new v3.0 app - it would be normal that the Gallery is empty until you start creating sketches or importing your files over from v2.x.
Here are links for more information on importing files over from iOS and Android: