There are some apps to help with this:
And you can look through the shopify apps:
If the shopper’s country isn’t one that you have a website for (and thus cannot auto-detect it and redirect to it), Reserved’s country selection screen could be a good option. But I’d recommend mentioning something to the effect that you noticed they appear to be in Canada, and that you don’t have a Canadian store – and to please choose a country from the list below. My hunch is that Reserved does not auto-detect your location (and they should).