I've had similar problems. Once they were swollen (have they done this?), I stuck them in those little Jiffy pots/greenhouse and put them in a warm window to sprout. I had little faith that they would grow, but out of 11 seeds, I got 7 babies (threw the other 3 out). 5 were City of Portland; 2 are Pink Futurity (only 2 of 5 germinated after 2.5 weeks). I have NO idea if they will mature true, but it's been interesting. I've gotten to the point where I've potted them in 4" pots and moved them outdoors, but the cooler night temperatures has stalled their growth. I expect them to get going once it stays warmer at night.

In the future, I'll stick with purchasing rhizomes and not mess around with seeds.

I tried nicking and soaking seeds as well. I did 5 seeds the first time, they all sprouted, but only 2 grew into small plants. I now have another 5 soaking and will pot them up soon. I change the water each day so that it is warm.

I prefer the tuber root as well. I've got lots of roots from last years canna. A friend gave me 4 roots for my birthday. Today I went to the local garden center and they had lots of roots for sale for 99 cents CDN each. So of course I picked up a few more that I don't have. Can't wait to get them all growing.

I'm going to keep special watch over the ones grown from seed to see how they do. Good luck with yours.

Here is a link that might be useful: My personal page about cannas - some photos of the seeds