Good topic. I sometimes try to move outside of box. But my question is not "what if Christianity is the truth," I ask "what does Islam and/or Christianity have in connection with truth?"
But then the question arise, which truth, or what is truth? Can I assess scriptures with my own view of truth, or with my own conjectures regarding truth?
The solution I think is that salvation is a personal process. God put a natural compass in us. But this is not a straightforward process. So scripture or religions are warning and reminder for the purpose of life, and guidance from God to how to live life according to His Will.
God wants us to believe in His Might and Oneness, and do good deeds. If we do this, label will not be that important.
But I also think that such a person will not be quick in rejecting true words of God, once he is addressed. So, if we can move out of the web of anxieties and conjectures, we will clearly see which Scripture is a perfect reflection of truth.
So far so good, I am content with my current stance.
[22.17] Surely those who believe and those who are Jews and the Sabeans and the Christians and the Magians and those who associate (others with Allah)-- surely Allah will decide between them on the day of resurrection; surely Allah is a witness over all things.
[2.62] Surely those who believe, and those who are Jews, and the Christians, and the Sabians, whoever believes in Allah and the Last day and does good, they shall have their reward from their Lord, and there is no fear for them, nor shall they grieve.
[57.27] Then We made Our apostles to follow in their footsteps, and We sent Isa son of Marium afterwards, and We gave him the Injeel, and We put in the hearts of those who followed him kindness and mercy; and (as for) monkery, they innovated it-- We did not prescribe it to them-- only to seek Allah's pleasure, but they did not observe it with its due observance; so We gave to those of them who believed their reward, and most of them are transgressors.