I've had a problem like this twice, where the guide wouldn't fit on the screen anymore. I called in to Cogeco when it happened the first time, and we got through it, but this time when it happened (a couple years later), I forgot how it was fixed.
Here's how I fixed it:
With the cable box on, press the Cable button (at the top), and press "Power", then after 1 second press "Menu". The "Pace User Settings" menu will appear. From there, enter the "TV Display Capability" section. From this list, all of my options were somehow set to "NO", except for the very last one "1080p60, which was set to "YES". Press the "OK" button on the remote to toggle. Just start turning the options back on, and your display should return to normal.