The first choice you have to make is ...
... do you want a
revolver or an
autoloader for a "backpacking gun"?
I really consider the two types of handguns to be "apples and oranges," so comparisons between their respective calibers (357Sig vs. 357 magnum or 10mm vs. .44 mag) is pointless. For me, it's an either-or proposition.
Having said that, if it's got to be a revolver, I'd go with a 4" .44 mag, because out in the deep dark boonies it's going to be more versatile, given what you might encounter, than a .41 mag, although the latter is what I'd prefer in other circumstances.
In autoloaders of reasonable size and weight - and you've expressed an interest in the G-20 - the
only serious choice for protection when camping or backpacking, or for "back-up" when hunting, is something chambered in
10mm Auto. No doubt whatsoever.
Since you've specified its role as protection when
backpacking, you want easy portability, and the G-20 with its polymer frame is going to fit that role better than, say, an all-steel 10mm S&W, Colt DE or Tanfaglio Witness (not knocking any of these).
I'd load a G-20 up with 10+1 (or, if you can access some prebans, 15+1) of Texas Ammo's 10mm/200gn XTP-HP load (doing 1250fps/694ft-lbs), along with a couple of spare mags of the same.
If I were intent on hiking into known bear country (large black bears or Grizzlies) and
couldn't take a rifle, I'd load up with TA's 200gn FMJ-FP (same velocity as the XTPs). (TA uses Hornady's 200gn 10mm bullets).
http://www.texas-ammo.com
Good luck.
HTH.