Why not try Cortifoam? I can't take Canasa either. I run to the bathroom right after or I wake up in the middle of the night miserable. Cortifoam is much easier to deal with, in my opinion. You don't feel the foam at all and it stops bleeding for me in a few days if I'm really diligent about using it and not skipping doses.
Have you checked in with your doc since trying the Canasa? I would call and see what s/he says.
UC for the last ten years
Current Meds: 6MP since 2006, Lialda, Asacol foam, Lomotil
Past Meds: You name it; I've tried it. (Asacol, Colazol, Pentasa, DiPentum, Rowasa, Canasa, Cortenema, sulfasalazine, Cortifoam)
Alternative treatments I have had success with: Acupuncture, Hypnotherapy