That's a story in itself that this post won't go into (I myself need to learn more about it). I haven't seen much else to connect Washington to the "deist" Voltaire. Though Tom Van Dyke's post on Voltaire reminds me of one quotation of Washington's that sounds quite "Voltaire like."
As Voltaire said:
This is the country of sects. An Englishman, as a free man, goes to Heaven by whatever road he pleases.
And George Washington writing to his French friend, Marquis de Lafayette:
Being no bigot myself to any mode of worship, I am disposed to endulge the professors of Christianity in the church, that road to heaven which to them shall seem the most direct plainest easiest and least liable to exception.
This kind of makes Washington sound like an outsider to the faith, which perhaps he was. But, nonetheless, such a sentiment perfectly captures America's ideal of pluralism and non-sectarianism.