Canon MX870 Series User Manual page 501

Click Specify... to set the document size and scanning resolution as required.
5.
Click Orientation... to specify the orientation of the documents to be scanned. In the displayed dialog
box, you can specify the Original Orientation and Binding Location. How to place the documents
when scanning the back sides depends on the Binding Location.
When setting is completed, click OK.
Scan Settings Dialog Box (Stack of Documents (ADF))
Click Scan.
6.