Heat a charcoal or gas grill to high for direct grilling.
Brush the shrimp and squid with canola oil, sprinkle with salt and pepper and grill until slightly charred on both sides and just cooked through, about 4 minutes for the shrimp and 6 minutes for the squid bodies and tentacles.
Combine the shrimp, squid, crab, peppers, celery, onions, olives, cornichon and parsley in a large bowl. In a second bowl, whisk together the vinegar, olive oil, lemon zest and juice, and season with salt and pepper. Pour over the salad and toss to combine. Cover and refrigerate for 30 minutes to allow the flavors to meld.