I have a 1987 Sunny 18 that I purchased used from a friend at work. It was in absolutely perfect condition. He said he and his wife paddled it three times and she felt uneasy about the stability. They were paddling it empty and are relatively small lightweight people (for Wisconsinites).
For a couple years the boat sat pretty much unused as I have several solo canoes that get used a ton, but then a friend and I were going for a 4 day river trip on the Wisconsin river and decided there was no better tool in my fleet than the Sundowner. We started using it for day paddles and couldn't believe what a joy it was to paddle empty. It's a genuinely fast canoe !
I am used to backpack style camping, bringing minimal gear (what's a sleeping bag?) and generally did the same in a solo canoe or kayak. We decided we had room to do luxury camping in the Sundowner including real folding chairs, a small gas grill and so on. We had a pretty good load going and I was a little nervous about how much less freeboard we had, but the boat paddled great with that 'big car ride' and we made exceptional time.
We even ran into some submerged logs and it handled it with aplomb. We took in a quart of water on a big incident, but the Sunny was very easy to handle in tough times and came away without even a mark. This year we did a similar trip covering 90+ miles in four days at a time when the locals were saying it would be tough going with the low water levels. We packed light to stay high in the water and by staying in the current and off the sand bars we were fairly flying.
I have 9 canoes and kayaks, and while my Wenonah Advantage solo canoe is still the one I paddle the most, the Sundowner is my favorite boat of the fleet when a good bow paddler comes along. I would consider it better suited as a day paddler for average to larger size people than to big gear hauling tripping, but for a bit lighter weight paddlers or if you pack reasonably it makes a fine tripper as well.
I recently purchased my Sundowner 18 used, and I have taken it out several times on the large lake that I live around. It is the standard Tuf-weave version. Overall, I am very pleased with this canoe. I find that it handles very well in both smooth and choppy water, and I was surprised at how well it can be turned for such a long canoe while still having excellent straight line tracking characteristics. The initial and secondary stability are both very good, although it might seem a bit tippy to the total novice, and the paddling ease, speed and glide are much better than one will find in the average run of the mill canoe.
It also holds a lot of payload, and compared to the Old Town Tripper which I previously owned, it is certainly a heck of a lot more fun to paddle! Amazingly, I have found that it even handles well as solo canoe as long as you don't try to go too fast. It is certainly not the ideal solo boat, but it is usable. The weight of my particular canoe is about 65 pounds, and I have little trouble lifting it, although I would probably want to shave off 10 pounds or so if I had to portage it for any distance. All in all, I'll rate this canoe a 10 out of 10, not because it is perfect, but because it is very versatile and does so many things so well.