Grid Display
To toggle the grid overlay on the preview image type Ctrl+G or select "Display Grid" from the "View" menu. Select "Grid Settings..." from the "View" menu to display the "Grid Settings" dialog, shown below:
Select the show print area checkbox to show the extent of a particular print size. For example most digital SLRs shoot images with an aspect ratio of 3:1 which fits perfectly on a 6"x4" print but needs to be cropped if it is printed on 10"x8" paper. You can display extent of a 10"x8" print by setting the print aspect ratio to 10 x 8.
NOTE: The grid display is only displayed on the preview image and doesn't affect images saved to disk.
Focus Point Overlay Display
To toggle the focus point overlay display type Ctrl+F or click on the "Display overlay" checkbox. When the focus point overlay display is enabled the seven focus point areas and the viewfinder circle are displayed over the preview image. Active focus points are displayed in red.
Focus points can be selected from the PC for all camera models except the EOS-1D and EOS-1DS. This is a limitation of the Canon SDK and may change in a future release.
NOTE: The focus point overlay display is only displayed on the preview image and doesn't affect images saved to disk.