Two sp3 (tetrahedral) carbons are created at this stage, which allows two different  diastereomeric possibilities of the halohydrin intermediate. The most likely result is due to chemical kinetics: whichever product is easier and faster to form will be the major product of this reaction. The subsequent SN2 reaction step proceeds with stereochemical inversion, so the cis or trans form of the epoxide is controlled by the kinetics of an intermediate step.
At this point in the reaction, two sp3 (tetrahedral) carbons are created, resulting in two possible diastereomers of the halohydrin intermediate. The most likely outcome is driven by chemical kinetics: the product that forms first and fastest will be the predominant result of this reaction. The subsequent SN2 step involves inversion of stereochemistry, so the cis or trans form of the epoxide is determined by the kinetics of an earlier step in the process.