Bring a large pot of water to a boil. Salt the water generously. Add the ears of corn and boil for about 5 minutes (3 minutes if using local corn during the summer). Once the corn is cool enough to handle, cut the kernels off the cob. Reserve the kernels in a large bowl.
After removing the corn, add the string beans and wax beans to the water. Boil until crisp-tender, about 2 minutes. Then transfer the beans to a bowl of generously salted ice water. Once the beans have cooled, transfer them to a paper-towel-lined plate and pat them dry. Trim the tops and cut the beans into 2-inch pieces. Add the trimmed string and wax beans, along with the cannellini beans, to the bowl with the corn.
In a small skillet over medium high heat, toast the coriander seeds until fragrant, about 3 minutes. Transfer the seeds to a spice grinder and pulse until finely ground. In a food processor, add the cilantro, lime juice, honey, ground coriander, scallions, garlic, jalapeno, 1 teaspoon salt and 1/4 teaspoon black pepper. Pulse a few times, and then stream in the olive oil while the processor is running. Add the dressing to the bowl. Toss and check for seasoning. Add more salt and pepper if desired.
If you don't have a food processor to make the dressing, you can cut the ingredients by hand and whisk them together in a bowl.