What is the religious ruling on a man marrying someone he does not desire, in fulfillment of his mother's dying wish, and must he complete the marriage?

A son is not obligated to fulfill his mother's will to marry a specific woman, as this is not a valid Islamic will that pertains to something the testator owns. Marriage is a matter concerning the son, and the mother does not own it. Even if the mother had ordered him during her lifetime to marry a specific woman, he would not have been bound by it, and it would not be considered disobedience. As Sheikh al-Islam Ibn Taymiyyah stated, parents do not have the right to compel their child to marry someone he does not desire.