I think the sentence should be "Google Map is different in different countries.", since there's one world map, but not many of them.
Even if we use "Google Maps", the copula should agree with the subject and become "are", but why it is "is"?
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The sentence as written means:
The service called "Google Maps" is different in different countries.
This could mean that the map looks different, but the differences referred to might involve other aspects of the service such as GPS navigation, local business listings, Streetview, traffic, or aerial imagery.
So the subject of the sentence is not the word "maps". It is an implied generic noun phrase such as "the service", "the website" or "the application". This implied noun phrase is singular, and so the verb is singular.
Here is another example which may be more familiar:
The Three Musketeers is a novel by Alexandre Dumas.
Here we are not talking about the three characters in the book, we are talking about the book. The book is identified by name and that name is grammatically plural, but this does not matter since there is only one book.
Returning to your example, if the speaker were talking about the actual maps displayed by the Google Maps service, he could say something like you suggest:
The Google maps are different in different countries.
In this sentence the word "maps" is a common noun and so it is not capitalized. The article "The" is not required, but it helps to make it clear that "Google maps" is not "Google Maps".
Though he might also see Google's maps as one big map. In that case we come back to the singular:
The Google map is different in different countries.
But I would stick with "the Google maps are".
Another option is to use the possesive:
Google's maps are different in different countries.
Remember though that these options may not represent what the speaker intended to say.