I'll confess that when I'm working on an actual historical fic (as opposed to comedy or crack, which is also delicious), and I have to choose between Hetalia-characterization, and my interpretation of a characterization that makes more sense in a historical context, I'll choose the historical one every time. 20%-ish of the people living in the colonies at the time were Loyalists, after all, and many of the Patriots felt more that independence was their only choice because King George wouldn't consent to let them represent themselves in Parliament or engage in limited self-rule, rather than wanting independence because they specifically wanted to be Americans. When you read the literature from the time, Britain was seen as an oppressor, but a beloved oppressor, if that makes any sense.

So, out of character for Hetalia, yeah. But I hope it makes sense as a historical interpretation and is valid in that sense!