Your case sounds fairly similar to mine, except I never had dysplasia: I had my colon removed 'cos of severe Crohn's which was refractory to all meds. I had ileorectal anastomosis surgery in July 2015, but the Crohn's quickly came back at the anastomosis. I went on Entyvio for a year, but I'm switching to Stelara.
You should have had biopsies taken during your scopes. What do the biopsies say? Personally if you have a history of Crohn's, then it is almost certainly that. Bowel surgery can make the intestines sore and swollen for a few weeks afterwards, but I have literally never heard of surgery causing inflammation 4 years later.
Before moving onto a biologic, you could try steroid or mesalazine enemas. If I recall correctly, Canasa is only 1mg but there are mesalazine enemas which are 4g. Bear in mind that mesalazine isn't terribly effective for Crohn's, so this may not work. But if the inflammation is mild it's worth a try. If it's more severe, I would seriously consider the Stelara. Side-effects are a possibility, but many people don't get any: just because they are listed doesn't mean they are inevitable.
Good luck with whatever you decide.
Dx Crohn's in June 2000. (Yay )
Tried: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, diets.
1st surgery 20/2/13 - subtotal colectomy with end ileostomy.
2nd surgery 10/7/15 - ileorectal anastomosis. Stoma reversed and ileum connected to the rectum.
Current status: Chronic flare. Do I have any other kind?
Current meds: 50mg 6MP; Entyvio (started 3/11/16)