Is it permissible for my maternal uncle, who is my mother's full brother, to marry my daughter?

Your maternal uncle is not permitted to marry your daughter, because he is an uncle to your sons and daughters. Every daughter of a sister is محرم (unmarriageable). This includes the daughter of a daughter of a sister, and the daughter of a son of a sister. The proof for this is the Almighty's saying: "Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, the daughters of a brother, and the daughters of a sister."