I'm trying to make an agreement with my ex. I told him I will drop the child support order now and file for my current husband to adopt my daughter. I said if he does not agree to the adoption and relinquish his rights, that I am going to file for child support again. But I just have one question... is that possible? If I cancel the child support order, will it be possible to file again if necessary?

It depends on how you did it. But generally one can revisit support arrangements.