US should just standalone.
Canada is kind of a "backdoor" to US, a NAFTA based power will cause unrealistic powerplay (eg, china begin increasing influence in canada for "peaceful" cooperation

)
besides, it would be cool to see someone try to take over the world with the canadian army!
Mexico is more tied to the United States than South America, even if they are economically more similar.
it would be economic disaster for USA, there is a reason Bush want to building a wall on the border: the cheap mexican labour will make american jobless and destroy the US economy. so it is quite hard to get the 2 population to unite behind a common economy.
*cough* only european are *cough* stupid enough to do so *cough* /jk!
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israel should stand alone.
- it is a provider of technology (eg. china, singapore, err USA?)
- it is able to make it's own war (nuff said!)
- it IS the holy land (

)
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as for the arab state, jordan and iran tend to take seperate path from the rest of the crowd (weariness of minority). and iraq is now(partially defunct).
so the arab might include libya, egypt, syira, saudi, maybe UAE?
Middle Eastern Coalition suggestion is good if you wanna make a strong islamic superstate; else the africa islamic state do have a grouping for their own.
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Iran and Pakistan should be seperate. afterall, if you wanna invade all the "axis of evil" it shouldn't lead to war with other arab or Pakistan (which is an ally in the war).
Pakistan and India as contenters of the indian subcontintent.
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ASEAN is not wanting to be trap by it's neighbour's sphere of influence. will play important counterbalance role of shifting slightly to the underdog while still maintaining neutral as not to earn the displeasure of anyone. it trys to balance the power of China, Japan, India and Australia (as well as New Zealand) and keep itself in the center of world trade.
Singapore, Malaysia, Thailand and Vietam are the key players. i suggest Kuala Lumpur as the Capital (twin towers

)
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east asia should be the 2 korea, 2 china and japan. mongolia is a problem, it has almost no army or economy to play an international role. it's dependency on china has growth since USSR fell.
however, the small size of having 2 korea and taiwan might be hard to play. should be a hit for players whom love 1 city challenge!
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the idea of Democracy Defense Initiative is a (GDI) joke right? taiwan is a chinese problem, it would be like giving china control of cuba and call it communist defense initiative; that is too cold war. neither the people of china, korea nor germany want to be divided. hope of unification like germany still remains.
besides, calling it a Democratic alliance is dangerous, if taiwan next election result is prounification; will it mean US and Canada will deliever taiwan to China?
also, the language US used on the taiwan president, to a level of threating abandonment if it continues it nonsense, shows that US see taiwan as a cold war burden; US is not interested in turning the island of taiwan into a country; it doesn't want war. if china unified peacefully, so be it. if not, US want to ensure stability; it no longer promise it will enter a war as it now fear that the taiwan leadership do something stupid and START the war instead!
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CIS as USSR basically minus the Baltic states. might want to remove those states near turkey and ukraine as they are no longer under moscow influences (see "no more cheap gas for you!" tactic used by russia!

)
central asia is still well under russian influences, china is increasing it's "coinfluences" via SCO; maybe interesting to have a central asia power; else it should be part of russian influence.
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I would like to see south africa and brazil as well, since they are part of the BRICS (Brazil, Russia, India, China and South Africa)