I would like to know if someone is making the intention to do ghusl medium istihaza, will my ghusl be inorder to make the intention I am making ghusl istihaza qurbatan ilallah or I have to say I make ghusl medium istihaza qurbatan ilallah?

Intention does not need to be spoken aloud but intention is that you are aware of what you are doing and that you are doing this action qurbatan ilallah (for seeking nearness to Allah).