Make the mayo: In a small bowl, whisk together the mayonnaise, paprika, lemon juice, and cayenne, mixing well. Taste and adjust the seasoning with salt and cayenne if needed. Cover and refrigerate until ready to serve. (The mayo can be made up to 4 days in advance and refrigerated.)
Make the crab cakes: In a medium bowl, combine the crab, mayonnaise, 1⁄4 cup panko, Old Bay seasoning, paprika, and salt. Using your hands, gently mix together the ingredients, breaking up any large lumps of crab, and feeling for any bits of shell that may remain. Divide the mixture into 6 equal portions, about 1⁄4 cup each. Shape each portion into a cake, and set aside on a baking sheet. Pour the remaining 2 cups panko into a wide, shallow bowl. One at a time, press each crab cake into the panko to coat evenly on all sides.
Preheat the oven to 200°F. Line a second sheet pan with paper towels. In a large skillet over medium high heat, warm the canola oil. When the oil is hot, working in batches if necessary to avoid crowding, place the cakes in the pan, spacing them about 1 1⁄2 inches apart. Cook, turning once, until golden brown on both sides, about 6 minutes total. Using a slotted spatula, transfer to the towel-lined pan to drain, and place in oven to keep warm. Repeat with remaining cakes.
Serve the cakes warm, drizzled with the mayo, with a wedge of lemon on the side.