I have been before the Committee of Adjustment a few times. Part of me understands it, but part of me views it as a cash grab that takes way too long and is just a needless roadblock. Never the less, it is what it is and it's not going to change. If you've never been, essentially, you go into a large room. Maybe it's the old council cambers, who knows, at one city hall or another and you make your pitch to a panel of 3 "judges". Hopefully you don't get a panel of social justice warriors who just want to say no to everything. You will be one of many people looking for minor variances in attendance on the day of your hearing.
Here's my advice on how to succeed.
1. Get your neighbours on board. This is MOST important. 1 neighbour who is opposed to your proposal has the ability to kill your proposal or at least seriously defer it. You need to get out of there with a green light. I would strongly urge you to get your plans drawn up and well drawn up at that by a skilled person. You need to have at least your site plan, floor plans, and elevations to at least 90% done. You should then take the plans and meet with your neighbours one by one to explain to them what you want to do. Bring pastries and beverages to the meeting even. Go over the plans with them in detail. Hopefully you get along with your neighbours. You want 3 neighbours on your left, 3 on your right, a couple across the road (like immediately across the road) and 2 immediately behind you. You want to do this BEFORE the city sends out the notice of hearing. If they are OK with what you are proposing, ask them to sign a form letter of support on your behalf. Write up a 1 page form letter that says that you have met with them, showed them the drawings, detail the changes and that they support you. If you can get these letters it will help your case. A LOT. Include the letters of support in your submission to the Committee.
2. Include photos in your submission to the Committee. In my case, I was tearing down an old shitty addition and I was exceeding the maximum lot coverage and violating minimum side lots. But even as my house was built in 1912, it violated all of that. When I went before the committee, I asked the panel to turn to the photos in my submission and I said, "all I want to do is tear down that crappy addition (and went on about why it was so terrible (which it was)) and instead of protruding 10' into my backyard, I want to go 16' and instead of 1 story, I want to build 2 stories which matches the original house" The lot lines are exactly as they are now and have been since 1930. With the photos, the panel was able to visualize exactly what I wanted to do.
3. Represent yourself, or at least be beside your designer. I represented myself because I did the designs myself and I had been before the Committee a few other times. Most people seem to let their designer do the talking, but I wasn't afraid to do my own talking. In my case, I had lived in my house for more than a decade. I told the committee, "This is my own house, I have lived in this neighbourhood for 12 years and I really like living there. I'm not doing this on spec, I'm not planning to flip this house, I just need a better house for my family and my kids, etc. etc." (I think at least subconsciously that they will give you the benefit of the doubt if you are the homeowner and not a flipper.)
4. The committee will then ask if there are any objections from the gallery. Now this is where it can get interesting. All of a sudden some guy you've never met jumps up and says he's opposed and why. If the Committee feels he has a valid argument, they will ask the 2 of you to go out in the hall and see if you can come up with a compromise. I've heard stories of unscrupulous neighbours doing this and looking for a bribe to get on side. On the other hand, you might just get a guy who doesn't want to see the changes you propose. Better for you is if you get a guy who even MENTIONS that he's sick and tired of all the renos going on in the neighbourhood and the associated dust and noise. If this happens, you're in luck. Try to get him talking about the inconvenience factor. The more the better. Then go back into the room and say to the panel that there is no compromising with this person because he is simply opposed to the fact that you want to build and the associated inconvenience. The committee is there to review your proposal as it pertains to the planning act and the zoning act of Toronto. Not to stop development because someone doesn't like construction. If however he is genuinely opposed to your proposal based on what it is, you have to find out where he lives. If he's far away, you can go back in there and say, "this guy lives 2 blocks away, but see those letters of support from my immediate neighbours, they are all on side" Lastly, you hear him out and you may need to decide whether or not you can or want to scale back your proposal. In reading about what you want to do, I would not care so much about your lot coverage, but I would have a harder time with you exceeding the maximum height restrictions, especially if it was out of character with respect to the neighbourhood.
5. Have comparisons. The committee works on precedent. You should be able to get from the zoning reviewer the typical lot coverages in your area that have indeed been approved by the committee. If you are in the range, you are golden. If you are more than the range, you will have an uphill struggle. What you will hear them say in the hearing is the word, "excessive". That's the kiss of death. If you hear them branding your application as "excessive" you are in trouble. You need to have a back up plan. As I said, unless you want this to drag out forever, as in a year or more, you want them to green light you on that day. So you need to have a plan B and say, "well, instead of 70% lot coverage, if I reduce this dimension to 20 feet from 24 feet, that would reduce my lot coverage to 62%, would that be acceptable? They would tell you that you need to submit revised plans obviously, however, at least you will know where you need to aim.
All in all, it is an adventure dealing with the City of Toronto for any sort of renovation. The problem is that between the Variance and the Building Permit, it's going to take you a year or more to get everything in order. The Building Department will not even start to review your drawings for compliance with the building code until you have your variance in hand and then they will do another zoning check and a structure check. BY LAW, they are supposed to either approve or deny your Building Permit Application within 10 business days. The reality is that they don't give a fuck and it will take 6 months or more. Expect to have to provide sealed engineering drawings for the structure, the trusses, the lot grading. Then you will need your architectural drawings. Everything has to be submitted electronically as well.
Good luck, you're going to need it.