To be clear...is the pot 3' deep? For a couple of reasons that is deep for growing out lilies, so once you have decided on the plant, hardy or tropical, you may want to add a platform to raise the depth to maybe 20". The 3' width is probably your limiting factor, as lilies with 3 foot spreads are fairly uncommon. From a practical standpoint....a tropical lily given ample sunshine will likely give you a longer bloom season. N. colorata or some of its hybrids....like 'Director George T. Moore' may provide more blooms over the course of the season.
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Craig