As far as iknow there is no restriction for a muslim to marry a christian girl, So i Think this is not a religous matter;
However,Cultural Differences are always a problem. Firstly/ You Cannot 'Make' her parents like you or agree to your marriage. I know you don't want to hear that,
Try to explain to his parents that whatever differences you & they may have,it means Nothing compared to the Love you have for their son. NEVER Disrespect them! But DO Stand up for yourself.
If you really love him try to win his parents
Try to convince them that whatever happens,you WILL Care for him & that married to you,he will never know hunger,fear,sadness!
Parents are parents no matter what,they wish always to see their son happy in his life.
Are YOU Prepared to change Your beliefs to win him If they ask? Is what you Are more Important to you than Your Love for him? Play up to the parents,Especially to the Father if he is the Head of their household. Be contrary,be Argumentative with them,Just Keep Trying!!