Although Rashi follows Chazal in identifying the angel which wrestled with Yaakov as the Sar (archangel) Shel Esav, the Yalkut Shimoni (132), Zohar Bo (51b), and the Pirkei D'Rav Elazar all identify the angel as Michoel or Gavriel. Why would he wrestle with Michoel or Gavriel!?
Radak (Gen. 32:25) explains that the man whom Ya'akov struggled with was an angel. He explains that God sent the angel in order to embolden Ya'akov in his struggle against Esav. Just as he was victorious in his first battle, he was assured of future victory.
ויאבק איש עמו... איש מלאך, וכן והנה איש עומד לנגדו (יהושע ה')...ושלח האל זה המלאך ליעקב לחזק לבו שלא ירא מעשו, כי לא יכול לו, לפיכך נאבק עמו ולא יכול להפילו, כן עשו לא יוכל לו
And a man struggled with him...the 'man' was an angel, and similarly "And behold a man was standing before him" (Joshua 5)...God sent this angel to Jacob, to strengthen his heart, that he not fear Esau; that he would not be able to overcome him. Therefore he struggled with him and was unable to topple him. So too Esau would be unable to overcome him.
Rabbenu Avraham ibn Da'ud writes similarly in Haemunah HaRama (II:4):
וכבר יראו לאנשים שהם מנוצחים מהם כדי להאמין אותם, וחזק את לבם כמו שבא בספור יעקב: ויאבק איש עמו
And they [angels] show people that they are victorious over them, in order to reassure them, and embolden them, as occurred in the story of Jacob: and the man struggled with him...
Shadal writes very similarly in his commentary there:
המאורע הזה היה ליעקב מאת ה׳ לחזק את לבו, להודיעו כי הוא בעזרו
This event happened to Ya'akov through God to embolden him, to make him aware that God was helping him.
R. DZ Hoffman also writes similarly in his commentary there:
מלאך שנשלח על ידי אלהים. היה צריך להראות לו ליעקב שהאדם המתהלך עם האלהים אף מסוגל לנצח מלאך או לפחות לא להיות מנוצח על ידיו.
An angel sent by God: Its purpose was to show Ya'acov that a man who follows God is suited to even be victorious over angels, or at least to not be defeated by them.
Hizkuni (ibid) provides a different very interesting explanation: that the angel was meant to prevent his escape from Esau, so that he confront Esau and be victorious; thus observing God's salvation.
ויאבק איש עמו: מלאך בדמות איש לעכבו שלא יוכל לברוח ויראה הוא הבטחות הקדוש ברוך הוא שלא יזיקהו עשו.
And a man struggled with him: an angel in the form of a man [sent] in order to impede him so that he would not be able to flee, [so that] he would see God's guarantee that Esau would not harm him.
This explanation is stated by Rabbenu Hayyim Paltiel (ibid) as well.