A - Thanks for the question. We must examine what the church teaches about matrimony before I can properly answer your question.
The Catholic Church teaches that marriage is a sacred bond between one man and one woman. It is Sacramental and creates an unbreakable bond while both spouses are alive. This bond is made by the consent of each spouse given to the other, which God seals with his grace.
If two baptized Christians wed, the Church views it as a sacrament. While the pastoral advice given to the couple in marriage preparation would be similar, faith issues are a bigger concern. This certainly means the marriage will have extra hurdles to overcome, but it does not make the marriage impossible. What should happen before a Catholic and a non-Catholic Christian marry is a sincere discussion of the issues and differences between them, including children, freedom of each spouse to grow in their faith tradition, etc. Also, permission must be sought and obtained by the Catholic spouse to marry a non-Catholic.
Thus, the Catechism says:
1634 Difference of confession between the spouses does not constitute an insurmountable obstacle for marriage, when they succeed in placing in common what they have received from their respective communities, and learn from each other the way in which each lives in fidelity to Christ. But the difficulties of mixed marriages must not be underestimated. They arise from the fact that the separation of Christians has not yet been overcome. The spouses risk experiencing the tragedy of Christian disunity even in the heart of their own home.
If a baptized Christian marries a non-Christian, the marriage is non-sacramental, though still valid. But, this creates a much bigger issue for the marriage. First, you must get a dispensation from the Bishop to marry a non-Christian. Second, the Catholic spouse must always, while still respecting the other spouse's freedom, seek conversion of the non-Christian spouse. The Catechism says:
1637 In marriages with disparity of cult the Catholic spouse has a particular task: "For the unbelieving husband is consecrated through his wife, and the unbelieving wife is consecrated through her husband."138 It is a great joy for the Christian spouse and for the Church if this "consecration" should lead to the free conversion of the other spouse to the Christian faith.139 Sincere married love, the humble and patient practice of the family virtues, and perseverance in prayer can prepare the non-believing spouse to accept the grace of conversion.Above all we should remember that any marriage will require open discussion, true love, faith, and selflessness by both spouses to be both good and glorifying to God.
From a practical stand-point, you must always take into consideration the fact that any marriage that contains such issues will have to overcome them somehow and has a smaller chance of succeeding. Thus, I recommend that one not enter into mixed-marriages lightly or without much prayer and discernment.