The process to set up Multi Currency Pricing with Braintree is different from other gateways. The currencies in Chargebee have to be mapped with the corresponding merchant account Ids in Braintree. For this, we require the mapping in this format - <Currency Code, Merchant Account Id>
Without the mapping every transaction from Chargebee will be processed through the default merchant account in Braintree. But once we map, Chargebee identifies the merchant account through which a particular currency's transaction should go through.
Furthermore, as part of the smart routing each payment method you'd need to link each currency to a payment gateway. For additional currencies, Braintree will appear as an option to link only after the mapping is done.