I might be dreaming, but the argument I would use is: does every vehicle in the ditch after a police officer drive by have a ticket on the window for careless driving?
If Jay, at any other portion of the road, just glided into the ditch on all fours, would he had been fined? Do the police follow tow trucks around? If a mechanical fault, such as a tire blowing, is the fault of the loss of control, is that careless driving?
With a driver's abstract mostly clean, it would be clear to show that x many years of driving, the experience I had, my observations, there was no indication that my vehicle would respond in the way that it did. The vehicle was out of control - I was not out of control of the vehicle.
Prosecuting on this is, as already been said, guilty until proven innocent. It really seems like they can pull anybody over at any time and premeditate that they might be in an accident no matter what they were doing at the time.
Unfortunately, you are in Ontario which, by the sounds of it, varies greatly from Saskatchewan. As much as the deducing what happened, that would be more at 'who is at fault'. In this case though, the whole incident is fully clear, except for the non-observable action just before the loss of control, which would be the point of debate. How, in a court of law, is the police officer going to prove you were driving with 'undue and attention' just before the accident? Just because you ended up in the ditch should not be enough, but since I don't know the precedents and etc... it may be enough.
It really seems this 'careless driving' ticket is really getting out of hand really fast, especially since every accident could be appended with one.