checkout currency not the same as website

[Mammouth]

Hello,

Default currency for mydomain.ca is CAD.

In Settings->markets i added USA pointing to us.mydomain.com with USD as currency.

When i shop on us.mydomain.com, all price are displayed in USD but when i click on checkout currency flip to CAD...

am i missing something in the config ?

I know i can force the language of the checkout page using javascript redirect like /checkout?locale=en but can i also force the currency ?

Thanks