I guess we'll know the answer to that when an announcement is made, which should be this week. Never under estimate the value of "last minute" negotiations. That said, i've been told that they chose which model they will order 4 weeks ago.
2010 for initial deliveries. For further details of their plans refer to this thread by Ha763 which carries the report that the above links got their information from plus a little bit more.
Of note, what has gone little reported is that CNAC and Air Macau plan to launch a rival to Viva Macau for much the same reasons. I understand it will be called Macau Express. It will be interesting to see how their plans develop too.