Scenario 1
while the aussies, americans, and iraqis weren't looking canada somehow acquired a few nukes, and detonated them in USA and therefore pretty much took over US.
Then they 'somehow' 'acquire' a anitmatter bomb and take the world hostage and iraq gives in, bu then a nation in like south america or somethin (like french guana) takes control of south america and allies with australia to dethrone canada.
or not
or...Scenario2
Some guy could decide to unite all the other countries in the world to fight the three superpowers, the name of this faction is the New World Order and Iraq gives in after Sadam Hussein 'mysteriously' passes away.
US, Austrailia, NWO FFA
(if you like these but not enuff, and you want more possible scenarios just ask
)