Plant canna bulbs at a fairly shallow depth. I'm sure there are lots of opinions on this, but for me, about an inch of soil above the rhyzome works. As for you, just plant the rhyzome at the correct depth. There are buds on the rhyzome that will eventually turn into plant stems. Keep those underground with the rest of the rhyzome. Now obviously, if the bud has grown and created a small stem, then by all means, have the vertical stem coming out of the ground. In the end, just make sure the entire rhyzome is under ground. Great plant the canna. Even if you mis-plant it. Chances are it will grow just fine.

Possibly classified as a weed in Australia. They're native to somewhere. C. indica is native in southeast USA. IDK what kind yours might be, besides lovely!

The only place bishop's weed works is where it is bounded at all sides by a root barrier (probably at least 10" deep.) Short of that, there is no way to contain it and it will spread rampantly (as you know!) You can spray it with Round-up and/or Weed-B-Gone. One of these two will get it, though I'm not sure if either one alone will get it. It also might take successive sprayings at 6-8-week intervals in order to know that roots are completely dead. I think it would be difficult to dig out because any root part remaining will start a colony again. As mentioned, you can also smother the colony from light with cardboard & mulch. Be sure to extend beyond the edges of the infestation. If you have a place where bishop's weeds works for you as a groundcover and you just need to control it, you could install 10" width roll aluminum flashing (from the roofing department) buried such that the width is vertical and the top is embedded in a healthy bead of concrete, concealed by a row of brick or pavers laid as a mowing strip.

I couldn't find the nuts until I dug down 8-10-12", which was an incredibly slow, laborious process in our dense clay soil. I broke a lot of shovels and trowels in our early years here. I often would find a lot of roots about 4-6" down beneath the plant, then just a couple of long skinny roots that went much deeper, and those were the ones connected to the nutlets. Once I was 12 or so inches down, I found long, skinny, horizontal roots running from one underground nutlet to another. Sometimes I'd follow the horizontal root for several feet before finding the plant it ultimately was connected to. It was just crazy. At that point, at least I thoroughly understand why it is so hard to get rid of nut sedge in a garden by digging. I suspect most people never dig deeply enough to find the nutlets. Of course, if you have nut sedge in a yard, you're going to have to use Image or Sedgehammer or something similar to kill it there because no one is going to dig up their whole lawn. Fortunately, I was only dealing with in in the fenced-in vegetable garden area. I am organic 99% of the time, but if I had to go back 20 years and deal with the nut sedge all over again, I'd buy Image or Sedgehammer in a heartbeat and use it because I spent too much time digging it out. I wonder now what I was thinking!