What would you do if you want 3rd kid but your spouse think that 2 kids is enough. We've already discussed it but it seems that he's not budging. I can't seem to change his mind.

If you feel strongly for it, try to just ask him to keep an open mind about it. Convince him by addressing any concerns he may have using logic and fact. For example, if he is worried that the family can't cope financially, show him how the budgeting can work out well (assuming that it is not an issue). Addressing his concerns will probably give you a stronger argument and at the same time, a good chance for you to consider if it is feasible to have a third child at this point in time.