In "The Official Ministry of Transportation (MTO) Driver’s Handbook", they said
It is illegal to drive in reverse on a divided road that has a speed limit of more than 80 km/h.
Is it legal to drive in reverse on a non-divided road that has a speed limit of more than 80 km/h?
The only specific prohibition of "backing" is at s. 157 of the Highway Traffic Act:
157 (1) No driver of a vehicle shall back the vehicle upon the roadway or shoulder of any highway divided by a median strip1 on which the speed limit is in excess of 80 kilometres per hour ...
However, there is a careless driving prohibition:
130 (1) Every person is guilty of the offence of driving carelessly who drives a vehicle or street car on a highway without due care and attention or without reasonable consideration for other persons using the highway.
And there is the Criminal Code's dangerous driving offence:
320.13 (1) Everyone commits an offence who operates a conveyance in a manner that, having regard to all of the circumstances, is dangerous to the public.
It would be misleading to say that it is absolutely "legal" or "allowed" to "drive in reverse on a non-divided road that has a speed limit of more than 80 km/h". It just isn't prohibited by s. 157(1) of the Highway Traffic Act.
1. Note that "divided" in the question was just a paraphrase of "divided by a median strip." There are many sections of road in Ontario that are not divided in that sense, with speed limits above 80 km/h, including much of the trans-Canada highway.
I would interpret the rules, including those that address divided highways, as saying:
It is unlawful to operate a vehicle in a manner that is needlessly unsafe.
Going backward on areas that are in or adjacent to traffic lanes with a speed limit of 80mph or higher is presumptively needlessly unsafe.
Situations may arise in which a vehicle would have no practical alternative except to drive backward for some distance on the shoulder of a high-speed divided road. If a collision occurs in the middle of the road and a motorist manages to stop just a foot or two before it, the normal prohibition against backing up would not be interpreted as forbidding the motorist from backing up to the extent necessary to clear the obstruction.
I would guess that rules about road design probably require the posting of speed limits below 80km/h on divided carriageways which are adjacent to parking spaces or directly connected to driveways. If a narrow driveway is connected to a road, it generally be expected that people would back from the driveway onto the road. Motorists should make reasonable effort to avoid traveling backward further than necessary, but there are generally no precise rules because it's imposslble to anticipate what courses of action would or would not be practical in every imaginable scenario.
