possibly most detailed maps of india can be found with mapmyindia, and with sygic its arguably the best GPS navigation available for india.
check here
Mapmyindia Sygic GPS Mobile Navigation Maps For Symbian Mobile Phones
i am getting the detailed maps and POI in city like kanpur and agra with sygic mapmyindia.
alternatively you can check Garmin (they are adding 200 more cities)
SatNav Map