Hi Michael,
Greetings from Syncfusion, currently we do not have support for cross hair in maps in our Xamarin suite, we are considering this requirement as a feature request and added it to our feature request list. While this feature itself is important, we cannot provide you a concrete timeline on this, so this feature will be implemented in any of our upcoming Volume releases.
Also, regarding your query "button on top of the map" can you provide us more information on this requirement so that it will be helpful for us to provide you a better solution.
Thanks,
Michael