Raw food v. wet canned food

Hello!
I am new to to this group but I am not new to feline diabetes. Mr. Sparkle was diagnosed in 2014. Started him on Purina DM wet food diet and Lantus insulin and within 1 year he converted! Yippee! Unfortunately the vet never warned me that it is quite common for cat's to revert back and become diabetic again...
He was doing so well for about one year and I had initially kept him on the Purina DM wet food diet. But it was becoming REALLY expensive and very inconvenient to even buy it because I could only seen to find it at vet's offices. Plus a case of 24 cans is really heavy to carry on the bus! So I did more research, through this forum and other websites, and found that raw food diets work well too with diabetic cats. So I started feeding Mr. Sparkle Primal Nuggets frozen chicken + salmon, advertised at containing 90% protein. He loved them, they are more affordable, I could buy them at my local pet store that had extended opening hours and a rewards program. He even seemed healthier in other ways, shinier coat, more energy. A new man! But then 1 year after switching to the primal nuggets he started urinating more and sure enough he was diabetic again. I did my own spot test at home, blood glucose was 29!
I brought him to the vet and he confirmed my suspicion that he is diabetic again. When I asked my vet why he had reverted, he wasn't sure. I asked him if it could be the diet, and he said maybe?? He said that, as a vet, he could not give me ANY advice on raw food diets because they are "unregulated" and suggested I go back to feeding Mr. Sparkle Purina DM wet... which he sells at his office obviously. There is nothing I want more than for Mr. Sparkle to convert again so I started him back on DM. He's doing well, we're down to 1U lantus twice a day, but he still hasn't converted.
My questions to you all, you fabulous fur parents, are as follows:
1) do you think the raw food diet could have contributed to Mr. Sparkle reverting back to diabetic
2) does anyone know where I could order Purina DM wet online that delivers to CANADA
3) does anyone here have success stories of their cats converting multiple times? I need a little hope
All comments are welcome!!
Thanks, Louise