Best neighborhood to stay in in Venice away from tourists

Parts of Cannaregio are pretty busy, but if you are north of Fondamenta Ormesini it is more quiet.
Alternatively eastern Castello may suit. It gets more quiet once you go east of the Arsenale.
In Dorsoduro, north west of the Rio Santa Margerita is quiet, next May we have an apartment booked just off Fond. Briarti and that works for us, staying 17 nights.
In a month, 22 September, I have an apartment for a couple of weeks close to the Frari on Ramo Cassetti, a street that will see only one tourist during that time, me.

hey hward
what are your dates and how many of you? we stayed in canareggio last year and san polo few years ago and loved both area.
aloha

We’re going end of March and there are two of us. My favorite thing to do is wander the neighborhood where we’re staying. So would love a fun area to explore with wonderful architecture and charm and places that are frequented by people who live there....

This place might work for you. Great apartment.
https://www.homeaway.co.uk/p6142339#summary

Castello is where you'll have the lowest percentage of tourists.

We stayed in the San Polo area and loved it. Our hotel, Hotel al Ponte Mocenigo, was just steps from the San Stae vaporetto stop off the Grand Canal. The whole area was quiet and charming. We loved to wander back the side canals to lovely Campos. A very popular restaurant, La Zucca, is close by as is Boresso, a cichetti bar, and Fontego delle Dolcezze, a good gelato shop. We would recommend a visit to Majer restaurant on S. Viacom dell 'Orio---a 5 minute walk from our hotel on the back streets. Alessandro, the chef, was the best! We would retreat to this area after battling the crowds around the Rialro bridge and St. Mark's Sq.

hey hward
we stayed at cabadoer-veniceflat.it loved the area, walked all over, got lost a few times, zigged instead of zagged, on an adventure. the couple that own it are fabulous, there is a small lift/elevator. near the frari church and could hear the bells ringing. our other place was a 2 bedroom in canareggio but there are places there that are good. i'll look at a couple things and send you later. off to watch my friends furry kids for the weekend.
aloha

We spent two weeks in the northern area of Cannaregio, near enough to access restaurants and sites but away from the fray and cruise ship tourist hordes. We were near Madonna delle Orta church.

At the end of May, we stayed in a flat in the Cannareggio. We were 10 minute walk from the Rialto in a small square whose only big noise was the school children walking through the square in the morning. It was lovely to have a break from the crowds, go shopping in the local grocery store, pharmacy.

Sandy

I vote for the Cannareggio area. We stayed there and loved it. We had Marriott points, so used points on their property in the area. The hotel felt like a small boutique place, right on a canal, and did not feel like a large-chain property.

As you move away from the main drags along the Grand Canal corridor, in any of the districts (called SESTIERI), the tourists dissipate like the San Francisco fog at noon.
Avoid also the San Marco district. That’s the busiest.
Castello has virtually no tourists as you move east far from Piazza San Marco.

Thanks to everyone for their advice! We're trying to figure out our trip and are now torn between returning to Italy and especially Rome which I loved, or going to Seville Spain. I was so sad to leave Italy in 2017 - SO sad! - and vowed to return but am asking myself if it's better to see something new. My problem is I think Italy has EVERYTHING - more than any other place I've visited. I worry that it sets too high a bar and Spain will disappoint. I love architecture, history, narrow winding streets, piazzas, flowers, good street food, gelato, etc. etc. Thoughts?

Can't do both?

St Elena way down at the tip of the Island (complete with vaporetto stop) is where you'll positively see the fewest tourists. There's a nice hotel there as well as some B&Bs and apartments. We love it there.