the keyless progression

so i came up this nice, chill progression. its got an Em7, Dmaj7, and a Cmaj7. i was thinkin that it would just be in the key of Em cause its basically Em, D, C only is sevenths chords. but not so because of the C# in the Dmaj7. so when im soloing and that chord comes do I just play a C# note instead of the C? or a C# instead of a D? or do I just plop a C# in the solo amongst the other notes?

Are you going for an atonal piece?

E Minor scale sounds good to me,i played your progression and i couldn't find any anomalities

EDIT:ok yeah,C# sounds weird,you may want to change the chord to a D7

Yea definitely E minor as a possibility. You could try out A minor as well. Shred some A minor blues over top as see how that sounds. You can try D major and B melodic minor as well.