As you should be aware Ontario is absolutely huge, so its broken up into WMUs (wildlife management uses). Some areas are bow only, some bow only with a controlled hunt (a shotgun only hunt that you have get drawn in a lottery to participate), and some ares have a two week rifle season.

As far as I can tell its mainly the populated areas, cottage country, and areas that have a major highway running thru it that don't allow rifle - safety reasons I guess.