If your TV has an "info" button, does the TV report the resolution of the signal from the STB to the TV?
If so, compare it with a channel that looks clear and crisp.
If they are the same, then the problem is upstream from your STB.
However, if the TV reports a lower resolution being received when that channel is being viewed, you might want to contact Cogeco. The fact the guide is looking different I find a fascinating detail.
DAB listener 12/2003-11/2011 (DAB Off-Air since 11/2011)
HD radio Listener since 06/2010