For vinaigrette: Whisk harissa and sherry vinegar together. Gradually add canola oil a few drops at a time, whisking constantly. Add olive oil a drizzle at a time, continuing to whisk and emulsify. Season with salt and pepper.
To assemble, combine crabmeat with shallot, lemon juice, and olive oil. Season with salt and pepper and carefully toss to combine.
In a large serving bowl, toss lettuce with fresh herbs and enough vinaigrette to delicately coat the greens (about ½ cup).
Carefully fold in crab mixture and serve with fresh lemon wedges and extra vinaigrette on the side.