If your horse is bracing against you either one or both of the following is happening: You are either too much in his face and not releasing in your hands enough, or he is numb to your leg.
Work on leg yields, shoulderfore, shoulder in, etc until he starts moving easily and willingly off your leg (so he doesn’t run from your leg, but actually moves correctly from your leg aid). As he starts to respect your leg more, he will begin to soften in his face when you use your leg to ask his to soften. Also, if he gets quick use half haults in your body, not in your hands, and make them really count so they do something, and then release. If he starts to brace don’t pull on his face, use half haults and your leg to ask him to soften.