You basically have two approaches here; you can compare text (which might be awkward if identical nodes are simply in a different order between files), or you can convert those to objects and write some sort of function to search for differences. It’s going to be somewhat tricky, but it’s certainly doable.
I think the first step would be to decide on the requirements. Using the two XML snippets you posted, what would you want PowerShell to produce as output describing the differences?