Mix peach sauce, white wine, and canola oil in a 2-cup measure, then spread over both sides of the halibut fillet(s) sitting in a plastic container. You'll probably need to cut the tail piece in half lengthwise to make two good size pieces. Sprinkle salt and pepper over the fish as desired. Cover container and keep in refrigerator for a few hours.
When grill is good and hot, brush the cooking grate clean. Grill fish fillets over direct HIGH heat (with lid closed as much as possible) until the flesh is starting to break into flakes and the color is opaque throughout, about 5 minutes per side. Break fish into 8 equal-sized pieces to fit the length of a tortilla.
Meanwhile, add shredded cabbage, salsa, and avocado, plus light mayonnaise and fat-free sour cream if desired, to a medium bowl. Toss to blend well.
After fish comes off the grill, warm tortillas a few at a time over direct heat with the lid open for about 30 seconds per side.
Assemble each taco by filling with about 1/2 cup of cabbage mixture and a piece of the fish.