I had a smaller crack in my plexiglass and I used plastifix as mentioned before. Fortunately, the crack was covered with the fiberglass skirt.
After many years of woodworking, one concept we used is "accentuate the flaws". At first, the concept is preposterous but the logic is when you decorate the flaws with other more elaborate details, people will notice the new detail as another design instead of noticing the original flaws. After you get your canopy fixed, you can decorate the canopy with painting over the flaws in the shape of a sunshade or cover it up with a sunshade pattern of dark tint. And if you embellish the new patch overlay with other interesting details, the crack magically disappears. It's funny how the mind works.
Good luck on the repair.
RV8 standard build: Empennage 99% completed
Wing -- Closed
Fuselage -- Canopy Done. Fiberglass 80%
Avionics Installation -- 90%
Firewall Forward -- Cowl completed. Baffle 90%
Electrical -- 90%
Donation paid through 2021