Amazon by Codisto include a free foregin currency management tool which allows you to list on overseas Amazon marketplaces where the local currency is different to that used for your Shopify store e.g. Your store currency is in USD but you've listing on Amazon Canada.

The default setting is for the currency manager to track currency rates and make pricing adjustments as the foreign exchange (FX) rate changes on a monthly basis but it's possible to change the frequency of the FX rate (price changes) or set your own custom fixed FX rate (that doesn't change).

Visit Settings>Currency Settings to make changes.