I do not think a single URL is going to be able to do that.
The Google Maps for iOS uses the comgooglemaps://
schema:
https://developers.google.com/maps/documentation/ios/urlscheme
And the Apple Maps app uses http://maps.apple.com
:
I think the best you are going to be able to do is give the user the choice, or just run with Apple maps since you'll know it's there (if there user-agent is iOS 6).