Ok, I have seveal thoughts on this.
First, is he only whining where his new brother is concerned or is he whining over EVERYTHING? If it is just in regards to his new brother, than are his concernes legitimate and just being presented wrongly? I don't know your family circumstances, but is there really some injustice between the two? Either real or perceived on your son's part? He may be asking you to bring the situation back into balance for him.
Next, please remember that whining is a passive form of rebellion. Here's what I mean. Your son asks you for a cookie before supper. You say no. If he were to then say, "you will give me a cookie NOW" you would be taken aback by his demanding a cookie. But if he says "Mooommmm, I realllly want a cooooookie" he has esentially said the same thing, just in a different way. He is not taking your 'No' as the final word.
My daughter whines a lot also. I got tired of telling her 'No whining'. Recently I started using a new phrase "Whining is not an acceptable for of communication". I repeat this to her every time she comes to me whining. It reminds her that I don't want to hear the whining and she knows that for me to answer her original question she must ask it without whining.
Also remember that most kids whine repeatedly because it works! Check yourself to see how often you are giving into the whine.