Does one have to cross the street so as not to walk in front of a church?
There is no obligation to actually cross the road, but one should keep a distance of four amos from the Church.
Sources: See Shulchan Aruch, Yoreh De’ah 142:10 and 150:1, and Rema 149:2. The obligation to keep a distance of four amos refers to a house of idol worship, and there is much debate among authorities as to the status of Christianity (if it is considered Avoda Zara, as Rambam writes, or not). Today there are hundreds of different of churches, each with its own belief and worship systems, so that the answer to the question will depend on the precise definition of the church.