Here is what you should do. Get your dog a little tie to wear on his collar. Go to the booth and ask them if they are hiring squirrel chasers. Take a breath, then say, actually he already has a job. He is my guide dog because I'm legally blind. My name is awesomesaucesaywhat and I just graduated from college with a degree in etc. and I'm looking for etc. Put everyone at ease with the guide dog and blindness issue right away, so that they can feel comfortable with you, and talk about you. You want to show them that you are OK with your disability. You are a regular guy like everyone else, and that you have a sense of humor about life.

Make your dog as presentable as possible. Sure up his training and discipline so that he is ready to be perfect. You can impress people with how well your dog behaves and performs. Be polite and kind while also being assertive with others about not interacting with your guide. Practice your confidence, but allow yourself to be vulnerable and ask for help locating and identifying booths. Use your experiences from being visually impaired to talk about the skills and knowlege you have gained. Don't let people ignore you, be assertive. Accept and embrace the fact that you will have to work harder than everyone else there to get taken seriously. Use it to your advantage.
Describe your visual impairment to potential employers by introducing your guide dog. It could be as simple as saying "Hello, I am (you) and this is my guide dog (your dog). He helps me navigate places and objects I can't see."
After that, lead with your interest in the job and your skills. They can ask about your specific visual impairment later, or you can explain after wards. Focus on your strengths, not your visual impairment.

Usually, there's a booth with representatives from your career center available to help you find out which employers are present (and often that info is online beforehand as well) and where to find them.

Come prepared with your resume and be ready to talk about your capabilities. For example, if you're really good at research with a certain database or if you've had experience that can relate to the company's objectives, make sure to casually humblebrag. I find that sometimes its helpful to mention these things initially rather than the elephant (or dog) in the room because it changes their first impression of you. Also, when i get to points where my visual impairment needs to be addressed, i usually briefly describe how i can use my assistive tech to accomplish whatever tasks i'm assigned, to reinforce my competance and value as a potential employee.

Bonus tip- sometimes school career centers offer pre-career fair workshops.


Best of luck to you!