Hi! ShipStation is still in the process of understanding the best way to address multiple currencies within a single ShipStation account. We greatly thank you for your patience as we work towards supporting this much-desired feature.Tim Mac Winepegsstore commented
Maybe try this:
If you are a bronze or silver subscriber you can create a manual store and import orders from a CSV file, Shipstation also integrates with Zapier.
What you can do is setup Zapier to connect with Shopify and automate exporting orders to google spreadsheet, convert the order currency to USD, then have Zapier automatically create orders in Shipstation from google sheets.