Answer: I think your idea of planting them in pots and keeping them in your screened porch is a good one. I'm a little confused about the behavior of your cannas, though. They actually grow well in moist soils and some even thrive in shallow pools of water. So, it might not be the soil drainage that caused the problems with your plants. Planting them in containers with fresh potting soil will certainly help them get off to a good start.
Best wishes with your cannas.
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