Hello. For a traditional solyanka, the choice of cucumber is actually crucial to achieving that signature tangy and rich flavor profile.
Standard supermarket cornichons are generally not ideal. They are usually pickled in vinegar rather than naturally fermented, and their small size means they lack the proper meatiness and depth of flavor needed for a heavy meat soup like solyanka.
Instead, you should look for large, naturally lacto-fermented sour pickles (often found in the refrigerated section of Eastern European grocery stores or specialty aisles). These cucumbers are brined with salt, garlic, and dill without vinegar, which gives them the necessary lactic acid punch. If you must use regular store pickles, make sure they are barrel-cured dill pickles rather than sweet or vinegar-heavy cornichons.