Ontario is already behind the curve for ATV access. Many Western states/provinces have limited access to certain areas for ATVs.
It's not rocket science. If you greatly increase the ability of a hunter to cover ground, chances are they will shoot more moose.
Rather than covering a few kilometers per day by foot, hunters on an ATV can cover dozens or hundreds. Combined with more road/trail access, this undeniably results in hunters being able to cover a larger area and increases pressure on the moose population.
I'm not saying ATV's should be banned or excessively limited. But it should at least be examined as a contributing factor to Ontario's moose problem.