Canon LBP7210Cdn Manual page 265

From the [Start] menu, select [Control Panel], and then click [Printer].
Windows Server 2008
From the [Start] menu, select [Control Panel], and then double-click
[Printers].
Right-click the icon for this printer, then select [Printing Preferences] from the pop-up
menu.
Display the [Custom Paper Size Settings] dialog box.
(1) Display the [Page Setup] sheet.
(2) Click [Custom Paper Size].
Specify the custom paper size.