What is the ruling on a Muslim man marrying a Christian woman in the West, and is it permissible for the mosque's imam to solemnize her marriage if her father will not agree, or must there be a Christian guardian?

It is permissible for a Muslim man to marry a Christian or Jewish woman if she is chaste. However, it is preferable for him to marry a Muslim woman of faith due to the inherent risks, especially in these times. The guardian (wali) of a Christian or Jewish woman for her marriage is her father. No one else may marry her off unless the father loses his eligibility for guardianship or unjustly withholds his permission (adhal). In such cases, the guardianship transfers to the next closest male relative who shares her religion and agrees to the marriage. If they refuse, then the Muslim judge becomes her guardian, based on the saying of the Prophet, peace and blessings be upon him: "The ruler is the guardian of whoever has no guardian."