At the ressurection, if God is going to reunite body and soul, which body will the reincarnated soul inhabit?

This question was asked long ago in the Zohar. 

"Rabbi Yosi answered: 'Those bodies which were unworthy and did not achieve their purpose will be regarded as though they had not been... [i.e. they won't be resurrected]. Rabbi Yitzchak [disagreed and] said: For such bodies the Holy One will provide other spirits, and if found worthy they will obtain an abiding in the world, but if not, they will be ashes under the feet of the righteous." (I Zohar 131a; cf. Zohar II 105b)

The answer, then, is that, basically, a soul is resurrected with the body it completed its final tikkun (correction) with, i.e. the one that was "worthy."