Back in the day, the bike club would cross every weekend. No big deal! No one paid any attention at all!
On the way back north, try to take cuts in the car line. It'll probably work well, you'll just get quizzed and waved through. "Are you a citizen OK get moving"
If there's any hassle, walk the bike through the pedestrian line. Again, zero hassle. I guess you could be asked "what's in the tool kit" to which you answer "tools" and get waved through. It's not like you're packing bottle rockets, or bottles of tequila, right?!
A generic answer: a guy I know was nervous, wondering what are they going to do? Don't worry, we told him, they're going to ask "what did you buy in mexico" and he had bought a bottle of tequila and a dress. We pulled up. "how you doing?" "bottle of tequila and a dress" "pull over, to that secondary lane"