mmmm delicious! carrots, imitation crab, bok choy and SPAM!
The problem with adding carrots to sushi is that it's usually too hard to put it in as carrot sticks. It's too crunchy-tough to chew compared to the rest of the stuff (rice, crab meat, cucumber, etc) and it throws off the texture of the sushi. Typically, you can get around this by manually cutting very thin carrots sticks yourself (time-consuming) or buying pre-shredded carrots (they look like match-sticks) which works but it's not ideal, they fall out easily after being cut because they're short pieces.
steamed carrots and bok choy
Here's the solution i figured out which allows you to use the carrots cut to the same size as the rest of the ingredients (size as in cross-sectional area). Steam them! If you have a steamer basket with your rice cooker you can steam them at the same time you cook the rice for the sushi! Here i tried it today, and it worked great! Interestingly the large, steamed carrots imparted a sweet flavor to the sushi.