Personally, it would have made more sense to have a Latin Empire in the south.
I assume it was the Latin Empire because its rulers followed the Latin (Roman) Church.
Yep, as opposed to the overthrown Orthodox rulers.
It is indeed supposed to be a reference to the Fourth Crusade, with the United States representing the Byzantine Empire, which was attacked and carved up after European (and maybe Asian too?) neo-crusaders attacked it.
The Latin Empire is the unpopular Crusader state set up after the Sack of Washington D.C., ruled by European nobility.
New York and New England can be compared to the Greek duchies, also under Latin rule. I'm not sure what Cascadia is closest to - maybe Thessalonica, or perhaps the cities of the Crimea.
The three
Byzantine American remnant states are California (Epirus), Atlanta (Nicaea) and Colorado (Trebizond).
North Mexico is the stand-in for the Sultanate of Rum, and so it is implied that it was established even before the Crusade. Texas is the rebellious Balkan states (Bulgaria? Serbia? One of those). Hispanic Florida is Armenian Cilicia, and Utah is, well, um, Utah (Albania, perhaps?)