The encounter is probably too easy
A level 8 character has an experience point budget of 450 for an easy encounter according to the Basic Rules. At CR 1/4, each wolf is worth 50 XP, with a multiplier of 2.5 since there are three of them and only one monk. At 375, the encounter will be lower than the XP budget for the monk. (This factors in the Party Size to encounter difficulty, but the modifier possibly should be a little larger since the monk is fully alone.)
Wolves do get Pack Tactics which makes them punch a bit above their CR, since they will all be attacking the same target1. In a larger party, the players might divide the wolves among themselves to prevent this from becoming as much of a problem, but gaining advantage allows the wolves to have a decent chance at hitting the monk.
With 17 or 18 AC, they would be hard-pressed to hit at all without Pack Tactics; the monk has even more thanks to the amulet. I would say the extra Armor Class and advantage about balance out, perhaps a little in favor of the wolves since they can actually hit, but they still deal very little damage. The monk can kill a wolf in one round with flurry of blows.
This encounter is a little too easy.
1: I have had many experiences where a few monsters with Pack Tactics that are meant to be easy to defeat end up almost killing a party member that they group up against.
If the goal is a fairly easy encounter, another wolf would probably balance things. Since the monk will probably kill one wolf almost immediately anyway, the encounter will be much the same. Except, the wolves get a chance for three attacks in the first round, bringing things closer to the easy encounter budget.
Note: Remember that Pack Tactics lets them punch up a bit since there is only one target.
I've included a few other encounters at varying difficulties that keep a similar flavor to the one you propose:
- Easy: 4 wolves (50 XP each * 2.5 = 500 adjusted XP)
- Medium: 2 dire wolves (200 XP each * 2 = 800 adjusted XP)
- Hard: 3 dire wolves (200 XP each * 2.5 = 1500 adjusted XP)
- Deadly: 2 alpha wolves (450 XP each * 2 = 1800 adjusted XP)
Note: My alpha wolves use the polar bear stat block, but have wolves'/dire wolves' ability to knock an enemy prone (see below) attached to their bite, and no swim speed. They will be a hair stronger than CR 2, but that is why the adjusted XP is lower than the 2100 budget.
If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.