Preheat your slow cooker on the Low setting.
Add the venison chunks to a large bowl. Season generously with salt and black pepper. Toss the meat with the flour until evenly coated.
Heat a large pan over medium-high heat. Add enough olive oil to coat the bottom of the pan. When the oil just begins to lightly smoke, sear the venison in batches until nicely browned. Transfer each batch to the slow cooker.
Lower the heat to medium and add the onions to the pan. Season with salt and pepper. Cook, stirring, until translucent, about 5 minutes. Add the garlic and cook 2 more minutes. Add the tomato paste and cook 1 minute, stirring constantly. Add the 1/4 cup water to deglaze, scraping up any browned bits. Transfer to the slow cooker.
Add the celery, carrots, potatoes, smoked paprika, sweet paprika, rosemary, bay leaf, dried thyme, and optional juniper to the slow cooker.
Pour in enough stock to just cover the mixture. Cover and cook on the Low setting for 8 to 10 hours or on High for 6 to 8 hours, until the venison is tender.