It will be highly dependent upon your budget...but if you are looking at a new Ruger made 45-70 then you should have a decent budget as these seem to be running somewhere between 2 and 3 thousand. So this opens up a wider field of possibilities for you.
Another thing not mentioned was if you also desire being able to hunt any other animals in any other type of hunting environment. If not, not a worry, but if so, you may want to expand the rifles capability a bit with a different cartridge with a little more all around capacity.
Deer and bears aren't usually hard to kill cleanly (average foot pounds recommended being 1000 ft lbs of energy at the animal for quick clean kills), but as with any animal, they can be individuals and some are just more tenacious of life. Older, larger, mature specimens can also take a bit more to kill quickly. Always best to plan for the worst and err on the side of safety with a cartridge with a little more energy (a larger caliber doesn't hurt either as it will provide more frontal area that just imparts more energy on the animal) and makes larger entry/exit holes for more bloodletting that allows for easier tracking. This is desirable on bears, as their loose skin and fat can cover wounds and leave less blood sign for trailing.
As stated already, any lever action from the 30-30 on up to the 45-70 will work for you at those ranges. At those short ranges, open sights will work well, unless your eyes are past resolving open sights properly (a condition that comes with age!). In this case, there are option for mounting scopes on most (but not all) lever action rifles you may look at. Another option is to mount a scope in quick detachable rings so you can take off if you desire to use open sights. Peeps and ghost ring sights can improve the potential accuracy of the open sighted rifle by extending the sighting plane.
Some favourites of many hunters here (excuse any redundancy in those already listed) may include:
Lever actions:
- Marlin or Winchester in 30-30; (or Henry, Rossi, etc.))
- Browning BLR in 243 Win, 257 Roberts, 6.5 CM, 7mm-08 Rem, 308 Win, or 358 Win; (they also have 270 Win, 30-06, 7mm Rem Mag, 300 WSM and 300 Win Mag)
- Winchester Model 88 in 243 Win, 284 Win, and 308 Win (the 358 Win is pretty rare);
- Savage Model 99 in 243 Win, 250-3000 or 250 Savage, 7mm-08 Rem, 308 Win, 300 Savage, or 358 Win (also pretty rare);
- Marlin or Winchester in 357 Rem Mag, 41 Rem Mag (pretty rare), 44-40, or 44 Rem Mag;(or Henry, Rossi, etc.)
- Winchester in 7-30 Waters, or 307 Win;
- Marlin in 308 or 338 Marlin Express;
- Marlin or Winchester in 35 Rem;
- Marlin or Winchester in 356 Win;
- Marlin or Winchester in 375 Win;
- Marlin or Winchester in 444 Marlin;
- Marlin or Winchester in 45-70;
Semi Autos:
- Browning BAR's in a variety of cartridges;
- Remington 740, 742, 7400 in a variety of cartridges;
- Winchester Model 100 in 243, 284 Win or 308 Win;
- Shotguns with rifled barrels in 20 or 12 gauge;
Pump Actions:
-Remington 760, 7600 in a variety of cartridges;
- Shotguns with rifled barrels in 20 or 12 gauge;
Single Shots: While they may have longer barrels, these rifles are quite often shorter than comparable rifles with other actions
- Winchester or Browning 1885 in a variety of cartridges;
- Browning B-78 in a variety of cartridges;
- H&R, Thompson Centre and other manufacturers in a wide variety of cartridges;
Bolt Actions:
- Multitude of manufacturers that make a wide variety of bolt actions in various cartridges in short, handy configurations that will suit your needs - I won't get into them all, but the older Remington 600, 660 and newer 673 were popular for this, as are the newer Ruger Scout rifles mentioned. Ruger made some other rifles over the years with shorter barrels as well. Remington's Model 7s were another option that came with 18 1/2 and 20" barrels, depending on year of manufacture. Options included cartridges ranging from the 243 Win to the 350 Rem Mag. Then there are the full stocked carbines popular with the Europeans, often referred to as "mannlichers" after the original manufacturer, in popular European cartridges, and the Ruger M77 or No.1 RSI (or International) full stocked carbines in a variety of cartridges.
Many offer rifles with 16-20" barrels that are handy in the stand, with sufficient power for many species that may be hunted. A trend seen today is for rifles with 20" carbon rifle barrels that are accurate, light, and handy.
In the end, handle as many as you can to determine which fits and feels best to you, and checks off the priority needs and desires in the rifle you are looking for, along with the cartridge that also checks of your priorities and meets your needs.
Best of luck in your quest!