Avoid using Activity implements OnMarkerClickListener, use a local OnMarkerClickListener
// Not a good idea
class MapActivity extends Activity implements OnMarkerClickListener {
}
You will need a map to lookup the original data model linked to the marker
private Map<Marker, Map<String, Object>> markers = new HashMap<>();
You will need a data model
private Map<String, Object> dataModel = new HashMap<>();
Put some data in the data model
dataModel.put("title", "My Spot");
dataModel.put("snipet", "This is my spot!");
dataModel.put("latitude", 20.0f);
dataModel.put("longitude", 100.0f);
When creating a new marker using a data model add both to the maker map
Marker marker = googleMap.addMarker(markerOptions);
markers.put(marker, dataModel);
For on click marker event, use a local OnMarkerClickListener:
@Override
public void onMapReady(GoogleMap googleMap) {
    // grab for laters
    this.googleMap = googleMap;
    googleMap.setOnMarkerClickListener(new GoogleMap.OnMarkerClickListener() {
        @Override
        public boolean onMarkerClick(Marker marker) {
            Map dataModel = (Map)markers.get(marker);
            String title = (String)dataModel.get("title");
            markerOnClick(title);
            return false;
        }
    });
    mapView.onResume();
    showMarkers();
    ZoomAsync zoomAsync = new ZoomAsync();
    zoomAsync.execute();
}
For displaying the info window retrieve the original data model from the marker map:
@Override
public void onMapReady(GoogleMap googleMap) {
    this.googleMap = googleMap;
    googleMap.setOnInfoWindowClickListener(new GoogleMap.OnInfoWindowClickListener() {
        @Override
        public void onInfoWindowClick(Marker marker) {
            Map dataModel = (Map)markers.get(marker);
            String title = (String)dataModel.get("title");
            infoWindowOnClick(title);
        }
    });