Firstly I don't think the sunflowers will provide the trellis. I think they are much weaker than corn.
Secondly, I haven't heard of anyone using sunflowers for companion planting. Maybe because they slow down the growth of other plants.
Sunflowers can kill. Of all the issues with sunflowers, perhaps the most interesting and dire is their tendency to repress the growth of other plants. This is because sunflowers are allelopathic – they exude toxins that stop nearby plants from growing. Have you ever noticed that the grass doesn’t grow underneath bird feeders? That’s why. It’s good from the sunflower’s point of view, since it leaves a wide open space every spring for new seedlings to grow. But it’s bad for gardeners who want to grow lots of different plants in close quarters. Most plants are affected at least somewhat, but pole beans and potatoes are especially susceptible and should not be planted anywhere near sunflowers.
They can blow over. Another of the negatives of growing sunflowers is their shape. Sunflowers tend to be tall, with big leaves and flower heads, perfect for catching the wind. A big storm can take one right out, and there’s a good chance it’ll take out the plants around it too.
Read more at Gardening Know How: Sunflower Planting Pros And Cons https://blog.gardeningknowhow.com/gardening-pros-cons/sunflower-planting-pros-and-cons/