How would you say the characters of Emily and Christiania are more alike than they are different in Cambridge?

You could make a case that Emily and Christiania, although vastly different women (from different parts of society), are taken advantage of, are smart, and are struggling with the superiority of the culture.  Their struggle is simply manifested in different ways.  In the simplest way, both women are abused or taken advantage of by Arnold Brown.  Christiania is raped by him, and Emily finally “surrenders” to him sexually.  The two women are also smart in their own way.  Emily is highly learned as she gathers material for a lecture series in England.  Christiania is learned as well, especially in the realm of the natural world with spells and enchantments. In regards to Emily’s struggle with the culture, she struggles in the choice of the “disgusting” Arnold Brown over any other the other beaus.  Emily also struggles with the abuse she sees among masters and slaves.  Any "obeah" in the town (which is simply a Caribbean sorceress) such as Christiania will always struggle with the culture in that he or she will always be seen as an outsider.  As a final similarity, the two women also make a kind of “escape.”  Christiania’s is a literal escape from the town.  For Emily, the escape is through having a stillborn child when Mr. Brown is killed.