Eis o código nota 10!
string apiKey = "Sua Chave Google API";
string urlgoogle = $"https://maps.googleapis.com/maps/api/geocode/json?address={CEP.Text}&key={apiKey}";
HttpClient clientgoogle = new HttpClient();
string responsegoogle = clientgoogle.GetStringAsync(urlgoogle).Result;
JObject jsongoogle = JObject.Parse(responsegoogle);
if (jsongoogle["results"].HasValues)
{
var location = jsongoogle["results"][0]["geometry"]["location"];
Latitude.Text = location["lat"].ToString();
Longitude.Text = location["lng"].ToString();
}