Tourism books recommend trying to blend in so you ride full throttle until five feet from the speed bump, the slam on your breaks. Repeat from the us border to tdf Mike Ps you could also ride slow, see the scenery, be safer and get rundown by an 18 wheeler! Just kidding, just stay right and keep a good eye on you mirrors. Pps smll durable bike like the Kwai Sherpa would be my recommendation.
I've been riding 2up on a KLR650 from Texas. Currently in Colombia and my passenger will be headed home. I wouldn't do the trip on a smaller bike, but now that she's leaving, I've considered trading for something as small as 125cc. Tons of people do the trip on the smaller bikes and parts/labor are easier to find. Big bikes attract a lot more attention, especially from cops, but they do have their advantages. I haven't ridden over 65mph once since Mexico and travel well under 50mph on most days.....South America may be different.