Looks like an easy one.
Average the brown bear and polar bear stats and remove Improved Grab.
Brown Bear: Str 27, Dex 13, Con 19, Int 2, Wis 12, Cha 6
Polar Bear: Str 27, Dex 13, Con 19, Int 2, Wis 12, Cha 6
Oh! They have the same stats.
In that case, advance a Brown Bear by 1 Hit Dice and remove Improved Grab?
So extra hit points and an additional skill point (in Listen).
To give us...
Amphicyon (bear dog)
Large Animal
Hit Dice: 7d8+28 (59 hp)
Initiative: +1
Speed: 40 ft. (8 squares)
Armor Class: 15 (–1 size, +1 Dex, +5 natural), touch 10, flat-footed 14
Base Attack/Grapple: +5/+17
Attack: Claw +12 melee (1d8+8)
Full Attack: 2 claws +12 melee and bite +7 melee (2d6+4)
Space/Reach: 10 ft./5 ft.
Special Attacks: -
Special Qualities: Low-light vision, scent
Saves: Fort +9, Ref +6, Will +3
Abilities: Str 27, Dex 13, Con 19, Int 2, Wis 12, Cha 6
Skills: Listen +5, Spot +7, Swim +12
Feats: Endurance, Run, Track
Environment: Temperate plains
Organization: Solitary or pair
Challenge Rating: 4
Treasure: None
Alignment: Always neutral
Advancement: 8-12 HD (Large), 13-16 HD (Huge)
Level Adjustment: -
These massive carnivores weigh more than 1,800 pounds and stand nearly 9 feet tall when they rear up on their hind legs. They are bad-tempered and territorial.
Combat
An amphicyon attacks mainly by tearing at opponents with its claws.
Skills
An amphicyon has a +4 racial bonus on Swim checks.
Should it retain this?
Regards
Mortis