Hi Wdpancoe! Thanks for posting in the Canon Community Forum. I see that you want to change the Scan Source for your PIXMA TS3522.
This printer does not have an Automatic Document Feeder (ADF). We do have other printers that have an ADF. The closest match would be the PIXMA TR4720.
The Rear Tray is used for loading blank sheets of paper for printing. It does not go through the scanner, but rather under it. It is not used for scanning.
If you would like a printer that does have an ADF, please make sure that Automatic Sheet Feeder or Automatic Document Feeder shows up in the printer’s technical specifications. Here is a link to the website for the TR4720:
https://www.usa.canon.com/support/p/pixma-tr4720
I hope this information helps. Thank you for choosing Canon.
