Users of SPD/DEF Bond 3

This post was about atk/spd bond so some of the examples are less applicable and some candidates for spd/def bond won't appear there, but it should give you some ideas
https://fireemblem.gamepress.gg/q-a/atkspd-bond-3

For general usage, I think that Healers can use it well since they don't have a lot of other options, but I don't know why they would want the extra Def. (Maybe to tank incoming Archers, but I really don't think that it's wise to purposely leave them in the range of Archers.) Units that typically stick together, like Armor units, might also make decent use of the skill, but I think most of them would prefer Distant Counter or Steady / Warding Breath, if the unit already has a DC weapon.

If you can't figure out who to give Spd / Def Bond, consider foddering for Kadomatsu+ instead. It provides the equivalent to a Drive Def 1 and a Drive Res 1 effects, which can be stacked with other Drives and Spurs, or effects from Corrin's Yato and Marth's Falchion, to turn your other units into beefy tanks.

Innate 1-2 range users like Zelgius

Sharena is a decent candidate due to her weapon having that same skill once refined. Nephenee is a great choice too as it also stacks with her weapon refinement, but Sharena will have both skills active in both phases, whereas Nephenee has her weapons effect only in enemy phase. A highly speed invested Chrom with his Bond refine could work out, making him hard to hit and improves his chances of doubling slower foes. Those are just the ones off the top of my head.