The Muslim husband who fears Allah should try his best to be just among his wives. According to the case in point, if the husband has made a promise to perform Hajj along with the first wife before marrying a second one, then he is supposed to fulfill the promise he has given to the first wife. If on the other hand, the decision to perform Hajj was taken after the husband’s second marriage then she (second wife) should be involved in the selection process through drawing lots.
Sheikh Ahmad  Kutty, A Senior Lecturer and an Islamic Scholar at the Islamic Institute of Toronto, Ontario, Canada, states the following: If the husband made a promise with the first wife prior to his marriage with the second one then he should fulfill that promise with her. Otherwise any decision for Hajj after the second marriage must involve the second wife as well. He is not allowed to pick one arbitrarily; he must rather be fair; if he picks one of them this time that should be through drawing lots; then he must also plan to take the second one later. Otherwise, it would be reckoned as unjust and sinful act on his part towards the second one.

Allah Almighty knows best.