Field #4 (Vessel): your vehicle license plate
I usually also put a short description of the vehicle in and the border guards have indicated that they'd also like to see "(Ont)" in it as well, so they can identify the jurisdiction the plate is from.
I also fill in the "Carrier's section" - carrier is "Self" and then I sign.
You also need to fill in the information of who the exporter is - your name and home address.
Once you get to the border, the Border Patrol Officer may also send you to X-ray ( they'll tell you where it is), or for further inspection.
They have the absolute right to do this and they wear guns, so do NOT argue with them.
-------------------------------------------------------------------
If there were in the world today any large number of people who desired their own happiness more than they desired the unhappiness of others, we could have paradise in a few years.
- Bertrand Russell
Imagination will often carry us to worlds that never were. But without it we go nowhere. Carl Sagan