George Washington Wouldn't Have Had a Problem with "The Shack":

From what I've read about it. I'm basing my views on the "orthodox" criticisms of this book. From the link:

For those who are unaware, it is critical to realize that William Paul Young espouses the heretical teaching known as Universal Reconciliation (condemned by the church since 533). This accounts for his heterodox views (e.g., faulty views of the Trinity, Biblical revelation, Christology, eternal punishment, etc…).

Every single above listed "heresy" was embraced by many "key American Founders" and the theologians and philosophers they followed.

I'm not sure if GW embraced "universal reconciliation"; I suspect he did. One thing we do know is he had absolutely no problem with those who did.

This is the link to the book's official website.