The primary reason I recomend a handgun rather than a long gun is speed of response.
Defense against wolves is likely to be a very close range proposition. Possibly too close to get a long gun into action and very likely too close to get off aimed shots with a long gun.
From what I know about wolf tactics, they tend to try to attack prey when that prey is injuired or ill. If forced to take on prey in better condition, they try to exhaust the prey prior to attacking. If, during an attack, the prey shows enough fight to injure or kill one or more wolves, they may back off and re-group, waiting for the prey to tire more. This assumes that they feel there is no other prey available. Please note: I'm not an expert on wolves. All I know is from various cable documentaries and internet searching.
Assuming what I think about thier tactics is sound (or at least close enough to be useable) then the defensive arm needs to be able to deployed rapidly, deliver enough wounding ability to seriously injure a wolf (not necessarily instantly kill one) and have enough capacity that you will idealy be left with ammo in the gun after the survivors retreat from the first rush. Note that if they don't reteat, it means you either killed them all or have become wolf food.
A .30 carbine, .223 or 7.62x39 has plenty of power to do the job and is available in guns with high enough capacity. However even the shortest are somewhat awkward in close handeling. The revolver magnums (.357, .41 and .44) are good choices from the power standpoint, but only the 8 shot .357s offer the minimum capacity I'd like to see and most all revolvers are going to be slower to reload (which you will want to do if given the opportunity). Magnum autoloader chamberings are limited. The only one currently mass produced (that I'm aware of) is the Desert Eagle and unless you have far larger hands than mine I wouldn't rely on getting the safety disengaged with one hand (and your other one may be occupied).
That leaves conventional autoloader cartridges. .460 Rowland, .45 Super, 10mm, 9x23, 9x25, .40 Super, .400 Cor-Bon, .38 Casull and .357 SIG are all excellent choices (some only if you handload). .45 ACP+P, .45 ACP, 40 S&W and 9mm can be good choices, but need more attention to bullet choice. In any of the calibers, I'd lean towards hollowpoints with reputations for deep or over penetration as a first choice and towards FMJ as a a valid second choice. I would avoid any of the light for caliber, pre-fragmented, or fragmenting rounds.