EDIT: Ooh, that looks interesting. What all is it symbolizing? The imperialists getting washed away by God to save America? That does certainly fit!
Other ideas: You could have Uncle Sam (or Justice) and Lady Liberty sort of stooping on one knee on each side of a shield with the Eye of Providence, kind of heralding God's watch over the Union (or Second Coming if you want to get creepy New Jerusalem antichrist-y about it
). They EoP symbolizes the RU dogma of Manifest Destiny in a nutshell, like God is watching over them on their divine mission to defeat all of their enemies. Manifest Destiny is one belief shared by virtually all Protestants in the Union, and it's the central tenet of America and the main reason for its existence.
Other than that, the main eagle is already clutching a cross in my rough draft, too, so I don't want it too bombastically plastered with more religious iconography, since the Union still has the traditional "'Murica, hell yeah!" red, white, and blue, Uncle Sam, and eagles everywhere. And they are a functioning republic, for now, and they do use some of the same secular symbols as OTL USA. EDIT: Although I do love that seal you just posted!