Is it permissible for parents to reject their daughter's suitor, who is religious and of good character, merely because he is of a different nationality, knowing that their daughter desires him and rejects others?

Difference in nationality is not a barrier to marriage. It is impermissible for a father to prevent his daughter from marrying on account of it if the suitor is a man of religion and good character, for the Prophet, peace and blessings be upon him, said: "If someone whose religion and character you approve comes to you to seek marriage, then marry him. If you do not do so, there will be tribulation on earth and widespread corruption." Likewise, it is impermissible for a father to force his daughter to marry someone she does not desire, for "a non-virgin woman has more right to herself than her guardian, and a virgin woman should be asked for her permission, and her silence is her permission." If the guardian insists on refusal or coercion, the daughter may refer her case to a Muslim judge to marry her to a suitable match.