Some people do experience steroid side effects on the steroid enemas. But more than that, long term use of steroids as a topical medicine anywhere isn't good - these will thin the tissue of your rectum if you use them for too long.
Rectal mesalamine is a great choice if you can tolerate it. Your experience with the Canasa might indicate an issue, but you did alright on the oral mesalamine (assuming the Lialda didn't give you symptoms of intolerance) so I think it's worth trying mesalamine enemas.
If you cannot tolerate mesalamine then I would suggest getting the steroid enemas and also getting on some other systemic med - your choice how to proceed with that.
The upper GI problems you described earlier in this thread sound like reflux, which you can treat with OTC antacids or ppis, also follow a low acid diet and eat small meals, etc. etc. Believe it or not, proctitis can trigger reflux.