According to interviews by both Wilder and Bettis, the Cannon deal came about as a follow up from our original interest in the summer, which ended up not being taken further because, ironically for this thread, we didn't have sufficient funding left to make a deal with Leicester (which at the time would have been another loan as I recall).
Wilder wasn't looking to pursue Cannon in January, until COH brought him up as a potential option. Wilder gave his blessing, the owners sanctioned it, and a short time later, we're £10million out of pocket.
Based on what people have said who would have been in prime position to know the exact course of events, it wasn't a case of Wilder proclaiming that promotion would be certain, if COH backed him in signing Cannon.
I think most people at the time, and everyone now with the benefit of hindsight, can say that the Cannon transfer was a mistake. We had other positions of greater importance to try and shore up (CB), and Cannon has not justified the price tag thus far by a long shot. But it doesn't appear to be the case that Wilder instigated the approach in January - he just agreed with it.