Mahendra,
Though I've not done this with Akamai specifically, we did a pointed setup for a few ISPs that did not seem to get updated on the GeoLocation db. Specifiying a given range for a specific ISP, and then designating the data center worked fine.
That said, if that data center had to come down for maintenance, yes, the GTMs, set to Topology, would then fail over to the other--but with an alternate as GA.
The only odd thing was if/when BGP would flap on occasion. We had to choose whether to let it flap some customers back and forth a bit during those times, or extend the time-out of Site A being recognized as down.
But to answer your question, Choosing Topology as primary with an alternate as Global Availability does allow failover. Works well.