Originally Posted by YOWgary

You'll get what you booked.

On a Business Lowest ticket with one or more segments seated in Economy, you will not be added to the upgrade list in advance or at the gate. If you see an attractive Business Lowest award fare pop up before departure, you can call in and change to this award, subject to any fare difference.

You will be eligible to use eUpgrades as if you had booked the Economy segment on its own, but I believe these book into Economy Standard by default.