I go across back and forth from Canada to the USA 12 times a year.
I live in Canada and always use my Nexus card
I always use the NEXUS lane regardless if I am using my personal or rental vehicle. Very rarely, but they do at random pull you in for a quick vehicle inspection. It is random selection.
Never had to pre register or inspect my vehicle ever.
2 Tips, never use your Nexus card if you have commercial products for sale or giveaway for business purposes.
Also never bring anything over for friends ect, only your items.
Both will cause you to lose you card!
For the above Tips, Use the normal lane and your passport only if you plan on doing.