I suppose it depends on your conditions (in the house) and how big a plant that you want to transplant. I usually don't start mine until about 3, possibly 4 weeks, before it can go outdoors. I wait until mid-april to early May, depending on when I get around to it. I don't transplant it outside until I am doing annuals at the end of May.

I think that you could probably put it out earlier than the end of May, but my yard it too mucky to work in much earlier than that. I think that canna can handle our May temps, just not my wet yard. I usually do 3 tall cannas and sometimes some shorter ones, so space is an issue in my patio doorway.

I don't use lights or anything for them, just plant them & sit them in the patio doorway which faces south. Depending on how busy I am with other things, the cannas are about 1 foot to at the most 2 ft tall when I put them outside.

The short ones (lately I have been buying these already growing) get planted directly into their pots and go right out onto the patio in the same pots. The tall ones go from the pot into the ground or into large whiskey barrels. They get much larger for me when planted in the ground.

I mostly use Rex Humbert, a dark-leaved one, which grows like gangbusters in my garden. Tropicana has been much less vigorous for me than good old Rex, whether in the ground or in a pot. I have a neighbor a few blocks away than grows some really great Tropicanas, but I sure haven't grown any big ones. In the ground Rex can get well over 6 ft tall, even in our short season. Tropicana is slightly more than 1/2 that size.

good question phyllis
last year was the first time i tried planting canna and i was very happy with the look it brang to my backyard.
However, much like the elephant ears they take forever to get going and look like anything substantial. I think I planted mine at the beginning of May last year and they were only about 12" high by the beginning of June. Our last frost date here is about the end of April so I may be starting mine indoors soon. From what I've read you can start indoors 4-6weeks before you plan to put them outside. But if you've got a great southern facing window indoors you could probably even start them earlier!