I'm glad you started this. I was going to do something similar. Here's what I do.
Because of where I live (tundra land, you know) I always start mine indoors around the 3rd week of March. If I don't, I never see blooms until the frost arrives. I came up with this method a few years ago and it's really worked well for me.
I start them in plastic, ziplock bags. They don't take up as much space this way as when you use round or square pots. I use plain old premoistened peat and put about 3 inches in the bottom of the bag. Make sure you punch some holes in the bottom of the bag for drainage. The canna goes in next and some more peat (an inch or two) on top. Moisten slightly and close the page. Put them in a warm place (light isn't really needed at this point) and watch for root growth. Once I see that, I start giving a bit more water and some very dilute fertilizer. Once top growth starts, I put them in the sunniest spot I have.
When you're ready to plant out, just cut the bag away. Cannas do not like cold, so make sure it's warm outside before you plant out. During the growing season, they like a lot of water and tons of fertilizer.
Here's a pic of some of the ones I have going right now.