Since any vegetative soil amendment would increase your soils ability to retain moisture are you sure you want to do that now? Is your soil now saturated with moisture and ddoes it retain that moisture during the growing season? What you may need are raised beds.

In my opinion, save your money. Skip the bagged potting soil (it's good for containers, but not much use in actual dirt), the bagged topsoil (there's no telling what's in it -- probably what you have already anyway), the peat moss (it doesn't add useful organic matter and is environmentally controversial), and the gypsum (it's good for sodic clay, but we don't have sodic clay). Instead, concentrate on adding organic matter. LeafGro is good. Dehydrated manure is also good -- if it smells, leave the bag open for a few days, and the smell will go away. Put the old mulch and leaves back on. And add more mulch! Preferably something that breaks down easily, like leaves and grass clippings, but bagged shredded hardwood is better than nothing. As Brent says, if you use mulch, you have to do a whole lot less weeding and watering, plus it improves the soil as it breaks down. I do understand your point about flower beds vs. mulch beds, but the problem isn't the mulch, it's the fact that some people apparently would rather look at a nice tidy bed of mulch than an untidy, colorful bed of flowers :-).

Cannas will grow in just about any soil. They are not picky at all, as long as they get adequate water and sun. They perform best in loose, well-drained fertile soil but they will grow in clay or sand or whatever you have.

I know this is VERY late - don't know if you will ever even see this posting at all - but for what its worth here goes. I am growing M. koenigii in fiber (fabric) pots. They have been in a mixture of either peat+bark (MM Soil pep in fact) + Growstone (GS2) or peat+bagged mix+GS2 Growstone when I couldn't get MM Soil Pep or anything like it any more. They were originally in a peat+bagged container mix when I started them from seed. It has been 3 years since they were potted up into the fiber plant bags and Growstone-based mix. Some were planted into a gritty-like mix - all of those have either been repotted into a Growstone mix where they are gamely struggling to catch up to their heartier brothers, or - they just flat out died. M. koenigii is a member of the citrus family, a cousin of the so-called "true" citrus such as lemons and oranges etc. I see no reason why what works for my M. koenigii wouldn't work for your citrus as well. You can get the Growstone from a hydroponics store. If they don't have it in stock, they should be able to order it for you. A 1.5 cu ft bag cost me around $35 the last time I bought one, a couple of years ago. That may seem steep at first but the stuff is easily recycled and reused, and it prevents compaction to the point where I've not had to repot for the entire 3 year period and will repot next spring only because most of the plants need to be potted up anyway. You want the middle size - GS2 - not the larger chunks nor the small gritty stuff sold for gnat control. Could be worth a try for you. Handing issues - it is dusty straight out of the bag, and since it is recycled glass, you don't want to breathe that dust. A 99c dust mask from Home Despot should be all you need. You need to rinse the dust off/out of it when you pop the bag open. Put it in a big tub of water and swish it around to de-dust it. If you're reusing/recycling - still put it in a big tub of water and swish it around - the spent organic matter will mostly fall to the bottom and you can just scoop the remaining Growstone into a bucket of bleach water to sterilize. I only sterilize when recycyling, don't see a need for it straight out of the bag. My initial mix proportions were 3:2:1 peat-bark-Growstone but that soon devolved to just mixing it all together until it "looked right". Especially after the MM Soil Pep wasn't available anymore and I was down to just peat and whatever bagged container mix I could find and afford that didn't have any sand in it and at least LOOKED like it had a fair amount of bark in it. It doesn't seem to have mattered, all my curry leaf trees that were initially planted into a Growstone mix at the same time (about 3 years ago) are roughly the same size and robustness. There may be issues of pH but if so, under my local conditions, it doesn't seem to have mattered. Plus all that peat moss is pretty acidic. But then my local water is pretty alkaline at about 9. At any rate it is working for me.