Yes, there is a way to set up canned responses! On a per document basis you can list the subject/body to pre-populate by going to Administration > System Initialization > Print Preferences. Click on the "Per Document" tab and you'll notice there's email information at the bottom of the screen:
This will pre-populate this text every time I email a Sales Order (you'll notice the drop-down at the top allows you to choose other documents as well).
Furthermore, a signature can automatically be added to an email as well by setting them up under Administration > System Initialization > Email Settings: