Whisk together the vinegar, mustard and honey in a small bowl. Whisk in the olive oil and season with salt and pepper.
Put the tomatoes, corn, cucumbers and onions in a large bowl, add half of the dressing and toss to coat; season with salt and pepper. Let sit at room temperature for at least 15 minutes.
Brush the bread slices with the olive oil, season with salt and pepper and tear into pieces. Chop most of the basil leaves, reserving some whole leave for rubbing the salmon and as a garnish. Just before serving, add the bread and chopped basil to the tomato salad.
Heat a charcoal or gas grill to medium high for direct grilling. Rub each salmon fillet on both sides with some of the basil leaves, brush with canola oil and sprinkle with salt and pepper. Grill until golden brown on both sides and just cooked through, about 3 minutes per side.
Put the salmon on a platter and drizzle each piece with a little of the remaining dressing. Top with the salad, drizzle with more of the dressing and garnish with basil leaves.