Shred the potatoes and onion in a food processor or with a grater or mandoline. Place in a strainer that has been lined with cheesecloth or a damp kitchen towel. Toss with 3/4 teaspoon salt and let sit over a bowl to drain for 30 minutes.
Gather the top of the cheesecloth and use your hands to squeeze out as much excess moisture as you can. Transfer the vegetables to a clean bowl; mix in the eggs, lemon juice, flour and some pepper.
Heat 1/4 inch canola oil in a large skillet over medium-high heat until shimmering. Working in batches so as not to crowd the pan, fry loosely packed rounded tablespoons of the potato mixture until browned, about 2 minutes per side. Add more oil to the pan and adjust the temperature as needed. Transfer to a paper towel?lined plate, season with salt and set aside.