Or HaChaim on Genesis 27:24/אור החיים על בראשית כ״ז:כ״ד

1 ויאמר אתה זה בני עשו He said: "you are indeed my son Esau" Isaac justified his bestowing the blessing. This verse is not a question. Jacob's reaction was a confirmation that Isaac was correct, of course.

2There is another meaning to the words אתה זה. Inasmuch as Isaac had thought up to that moment that the voice indicated that Jacob stood before him, he now pointed at the body of the person before him saying: "you are Esau" seeing the hands had convinced him. When he articulated the blessings he concentrated on the person opposite him without regard to that person's name. This actually made Jacob the true recipient of the blessings, even though Isaac had made mention of Esau. At the time of the actual blessing Isaac concentrated exclusively on the person in front of him.