It seems that the wise and all knowing CFO's

have got together and determined that an auto is not a suitable tool for shooting bears, so they no longer allow them on ATC's. Thus pistols are out of the running and we are left with revolvers. While you can find a .45 ACP revolver like the S&W and Colt 1917's or the S&W M-25, and stoke it up a little, a hot loaded .45 Colt out classes the .45 auto, and the .44 magnum for that matter.
From your list that leaves the .357 and .44 magnums. I have both on my ATC, but I don't consider the factory loads in either gun particularly useful. I load a hard cast 325 gr WFN or the 300 gr Sierra in the .44. Likewise in the .357 I found a heavy for caliber cast bullet, a 195 gr SWC. Both of these bullets penetrate well and leave a good wound channel. Velocity is about 1150 fps in both guns.
The cartridge needs to combine bore size, bullet weight, and velocity to ensure effectiveness, but should not be so powerful that a fast followup shot is impossible due to the heavy recoil. For this reason I would load down very powerful rounds like the .475 Linebaugh or .500 Wyoming to tolerable levels. There is a difference between a hunting round and a defensive round, and there is a difference between the hunting handgun and the defensive handgun. Defensive guns need to be small enough to carry daily while you carry out other duties. The hunting handgun is a hunting tool that can be as bulky and heavy as a light rifle.
When choosing a handgun for wilderness carry there are some considerations to keep in mind. First is the gun will be exposed to knocks and bumps, rain, snow and dust. Most gun savvy folks would recognize the value of an auto in a harsh environment, but we are left with the delicate lock work of the revolver. On the plus side though, revolvers are generally generally more powerful. There should be nothing delicate on your ATC gun. If your gun has an adjustable rear sight it should be changed to the type that uses opposing screws for windage adjustment, rather than a spring and adjustment screw. Check out the Rough Country Sight from Hamilton Bowen. The grips should come as close as possible to fitting your hand, but should not be larger than necessary resulting in the gun getting in the way all the time. Grip material should be resilient to hard use, and after market micarta grip panels are superior to most factory wood grips.
The ATC requires the gun to be carried in a non-concealed manner. Some folks like across the chest holsters or shoulder holsters. In my world an across the chest carry is asking for a broken gun, and if the gun was back under my left arm I wouldn't be able to reach it. I prefer a good quality leather belt holster worn high on the strong side. The bulk of the gun is tight to my body under my rib cage and is subject to fewer bumps than if I wore it on my hip. A proper holster should cover the trigger guard and rear sight. A thumb snap restraint is a good idea, but both of my holsters have a strap and I haven't yet been mauled because I couldn't get the gun out. On the other hand, considering why you are carrying the gun, I don't think that the additional protection provided to the gun by a full flap holster is an acceptable trade off to the loss of speed. I prefer an open muzzle so that ca-rumba that collects around the gun can just fall out of the holster rather than collect at the bottom. What I considered the best field holster was the Bianchi Cyclone, but it is no longer available. This holster offered good protection to the gun, could be worn strong side or cross draw, had an open muzzle, and thumb snap restraint. I highly recommend blocking the holster so the fit to the gun is mirror image. This protects the finish of the gun and prevents it from hanging up when you draw.