Heat a large saucepan over medium-high heat. Add ½ tablespoon canola oil to pan, and swirl to coat. Add onion and garlic; sauté 5 minutes, stirring constantly.
Add sugar and the next 9 ingredients (through plums); bring to a boil. Reduce heat, and simmer, partially covered, for 30-40 minutes or until plums break down and sauce thickens, stirring occasionally.
Remove from heat. Give it a taste and adjust if necessary adding a sprinkle of kosher salt or a little more sugar if needed for sweetness.
Preheat oven to 450°.
Heat a large skillet over medium-high heat. Add ½ tablespoons oil to pan; swirl to coat, adding more oil if necessary.
Sprinkle pork evenly with salt and black pepper. Add pork to pan; sauté 7 minutes, turning to brown on all sides.
Transfer pork to a foil-lined jelly-roll pan; coat with about ½ cup plum sauce and use a spoon to spread it around on the pork.
Roast pork at 450° for 15 minutes. Remove pork from oven. Turn pork over; coat with an additional ½ cup plum sauce.
Roast 10 minutes or until a thermometer inserted in thickest portion of pork registers 155°. Remove from pan; let stand 10 minutes. Slice crosswise. Serve with remaining plum sauce.
