How can I hang canvas curtains on a semi-circle patio cover?

If it were my house, I would call a wrought iron guy or gal and have them come out and make custom rods. You put all that work into a beautiful space, you do not want anything ticky tacky. Maybe add some decorative corbels to tie the look together.

I have had problems uploading photos too, you are not alone!

the best answer is to get a custom rod curved to your specifications but that could get pricey. Another way is to use multiple short rods. You would need to slit the back of the curtain to bridge two butted rods

Would half of a hula hoop work?

Have you looked into flexible plumbing supply pipes? I don't mean the rigid PVC. If you used enough bracket supports I guess you could hang canvas.

Another thing is electrical conduit. There is a tool that will bend it into curves but it is a specialty tool and not something most folks have hanging about, but maybe you could rent one.

inexpensive conduit pipe and a pipe bender will do the trick