Most likely what will happen after topping is the plant will fork into two large branches at the closest node to where you topped the plant. The plant will still try to grow mostly upwards with these two branches, and they'll probably grow their own suckers. This is assuming your plant is indeterminate.

I usually don't have much luck with topping off a plant, then trying to root the cutting from that. I'm sure its possible but I usually just throw it in the compost bin.