Heat canola oil over medium-high in a large saute pot. Add onion and garlic and saute until the onions begin to turn translucent. While they are cooking, season the flour with salt and pepper and coat the oxtails, allowing any excess flour to fall away. Sear the oxtails on both sides in the pot with the onions and garlic, then remove them to a utility platter. De-glaze the pan with the red wine. Whisk in demi-glace and tomato paste and add bay leaf, parsley and thyme. Lower heat and return oxtails to pot. Cover and let simmer until meat is tender (it should easily fall away from bone), about 3 hours. Remove oxtails to a platter, cover, and let rest in a warm place. Strain braising liquid into another pot to make it into a sauce. Spoon off any excess fat that may be on the surface. Increase heat, allowing the braising liquid to reduce by one-half to two thirds.
Combine the Gremolata ingredients and set aside.
While the sauce is reducing, prepare the toasted French bread. Preheat the oven to 350 degrees F. Brush the olive oil on the bread and sprinkle with garlic powder. Lightly toast in the oven.
Remove the reduced sauce from the heat and whisk in the butter. Spoon sauce over oxtails and top with a small amount of gremolata. Serve with toasted French garlic bread.