I've been to Central Toronto Veterinary Referral Clinic on Eglinton several times for different reasons with my kitties & I have always been impressed with Dr Ho. I'm not sure about her experience with Diabetes but I'm sure you could call & have a quick chat with her about it to see if she's someone you'd like to take your kitty to. She saved the life of my cat Oreo & also of my Mom's little dog so I don't hesitate to drive the 2.5-3 hrs there just to see her. You only need a referral from your regular vet the one time & then you can just go when you need to after that (at least that's been my experience).
Don Mills Veterinary. I was referred there from Edmonton but that was a very long time ago. They started in a house and then got bigger but Doctor Handsome/Randy is still there. Sometimes it's the staff that can make a good or bad impression. At that time (pre-internet or Yelp) there was some kind of rating system which is no longer in use. I'd avoid the high priced matching smock wearing clinics right downtown. If you ever move to Milton I have the world's best vet but that's quite a hike down the 401. http://www.donmillsvet.com/about-us/team/