What is the best way to determine the country/currency for a user?

I am using a similar set-up as gorails - devise for registration and stripe for subscriptions. I have separate plans for each currency were are going to market to (USD, CAD, GBP). But I want to offer up the subscription options to the user in their currency - what is the best way to do this short of asking them - what country do you live in? I would like to make an intelligent guess and then allow them to change it if needed.

Check out the Geocoder gem => https://github.com/alexreisner/geocoder and http://stackoverflow.com/questions/34816490/get-remote-ip-address-in-rails-model

What you'll want to do is snag the IP in the controller with something like
@request_ip = request.ip then geocode @request_ip for the country.

You can really use just about any geocoding service that can do the ip address to physical address conversion.