Is「天佑美國」the correct translation for "God Bless America"?
According to Wiktionary, 保祐 is a variant of 保佑. Google Ngram Viewer also consider 天祐 to be the same as 天佑: Ngram

Actually, here in mainland China, I think 佑 is much more prevalent than 祐 (I have not been to other Chinese-speaking areas so I cannot give you a definitive answer). You can witness it from the Wikipedia translation of similar subjects, all of them use 佑 instead of 祐:


God Bless America - 天佑美國
God Save the Queen/King - 天佑女皇/女王、天佑吾皇/国王
Gott erhalte Franz den Kaiser - 上帝保佑吾皇弗朗茨/天佑吾皇弗朗茨


So if you have to choose between them, I'd say 佑 is actually a safer choice.