Will the US government ever give Edward Snowden a fair trial for the charges against him?

They aren't going to change the charge.  He committed treason as far as I'm concerned and, if he doesn't want to live wherever he is now living, he should have considered the consequences of his actions before he did it.  He can rot there for all I care or come back to the US and face up to what he did and serve time in prison.

Fairness has nothing to do with the charge.  The government has to prove what they allege he did and, if they prove their case, he will be sentenced.  If they can't prove their case, he will be found not guilty.  That's what is "fair."

The nature of the charge CANNOT be the reason a trial is not fair. That said, as long as he stays in Russia, he can't receive a fair trial in the US.