Based on what he's shown for us so far Cannon reminds me a bit of both Brewster and Ched Evans. They can all strike the ball pretty well, but seem to get few chances and their pace let them down. You could even include Billy Sharp (1st spell) in this comparison.
Evans got his break by us dropping down a level, and maybe that's what could have reignited the careers of Brewster and Cannon as well. Of course, Evans blew it all after a night out in Wales. Sharp really made the most of his career. Over a long career, he wasn't too proud to drop down a level, which he did a few times and came back stronger.
But Brewster has hung around with us for too long, to the extent we put him in different positions in the desperate hope he'd contribute in some other way, even if not scoring goals. As he matured he managed to improve from 'dreadful every time' to 'ok on the odd occasion'. Us offering him new terms suggests we're still not prepared to accept our expensive mistake.
Cannon should be able to score many goals at some level. Hard to say if he'll ever do it for us, or at Championship level in general. So far defenders catch up with him and comfortably get blocks in, in a similar manner to what Championship defenders did to Evans and Brewster. If the goals don't start coming pretty soon we should probably reconsider our faith in him.