What is best practice for EE lives & works in Canada company, but also gets paid in a US company?

Hello,

We are looking for the best practice on how to handle an employee that has a Canada home company, lives in Canada, salary in Canada company but also gets paid a bonus in a US Company. [all paid in USD]

We currently have him with only one AB# and then HR/payroll flips him to the US co & US SSN to pay his bonus, then flips it back to Canada; this often leads to tax issues because the variables don't always get flipped back correctly. Is it best to create two AB#s for this person since he has a CA SIN and a US SSN? Looking for best practice and/or suggestions to streamline for accuracy... it always seems to end up a tax mess at year-end!