CAN-USA cross-border transfers

Hi, we're looking to compare processes with other companies that use PNA for both CAN and USA and have employees that transfer from one country to the other (and sometimes back again). Does the employee retain their EmplID, or do you create a "new" employee in the new country so payments for that EmplID are only a single currency? How do you handle payments in the old country/currency after the employee has transferred and been paid in the new country/currency? (an example is a bonus earned while working in the old country that isn't paid out until