How can I block shipping to canada and international orders

How can I block shipping to canada and international orders for specific shops? The shops that only ship to the us?

Merchant question: I do not include shipping for Canada or international orders, as those need to be weighed and calculated for each individual order. It's unclear on your site regarding Canada and international. If shipping is left blank, do they ship for free, or will those countries not be included as shipping destinations? It's not clear.