If my dad married 3 days before his death, is his wife entitled to his estate and/or his belonings?

If your father did not have a will then his whole estate will be distributed intestate. Three day marriage although short, is still a valid marriage and his wife is still entitled to some of his estate accorinding to MN intestate law. How much she will get, however, depends on MN state law. You should consult a local attorney to find out.