I got in an argument with a buddy of mine over whether the chord progression I had written was in C Major, or A Minor. I've read up on what makes it one or the other, and I strongly feel it is C Major.
F(add9) Dm7 Am G Csus4 C Am G
You give us neither the G7 > C or E7 > Am cadences that would answer your question conclusively. Which way will you choose to end the piece of which this is an excerpt? Neither you or you friend is wrong, or right!