Shopify multi currency best practice?

I have a Shopify store that sells in Canada and USA. it's located in Canada with CAD as it's main currency.

Using shopifys built in markets, I can change the domain based on the country. So my question is.

Do I go with .com in USA and .ca in Canada? Or .com in Canada and .com/en-us in USA?

I've never used to different domains for one site so not sure that's good? Didn't even know it was possible but Shopify tells me it is.

Btw, I can't do .com in USA and .com/en-ca in Canada for supplier reasons.

What do you guys think?