I have crossed the us/canada boarder 4 times on two streamlined motorcycles. They ask me to take off my helmit look at my passport then ask me where I am going and how long I will be in the U.S. They then ask about the reason for my travel to the states and If I have fire arms, drugs or fruit. They then ask about the bike, at which point I tell them what my fuel consumption is and answer any other questions they have. On occasion at/when boarder crossings that are not buisy I give them a mini tour of the bike and the reasons for the variouse parts.
Coming back into Canada they ask how long I have been in the states and how much I have bought and if I have had work done on the bike. They also ask that I remove my helmit and check my passport.
They do have the right to search your vehicle and they do that if you give them cause and/or randomly. You are not allowed to bring fruit into the US and the agriculter guy will confiscate your oranges.
I have also crossed the us/canada bourder in my Yaris that has a belly pan and the experiance was the same they did not care about the upper grill blocker or the belly pan.
They will also ask you if you have a criminal record or if you have been finger printed.