GTK interaction with Google maps

We are trying to make a GUI application in C using GTK that would use google maps api to download a map and find the shortest path between the source and the destination. We have implemented a mini web browser in our application using web toolkit. What is troubling me determining how would our application interact with the google maps api and how to go about running our algorithms(say Djikstra's) on the map the we downloaded. Any help is appriciated.

You cannot do that with Google Maps as they do not offer a vector api to download. However, you should look at OSM which provides that. libchamplain should be able to do that for you.