This will not help you at all! I have president, I think. Almost 20 plants, and all are different height. Some are almost 5 feet tall, and others are barely 2 feet.
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From left to right, you can see they get smaller.

Is it possible that the ones on the left either get more water or better soil or something? More sun maybe? My Wyomings actually are different. I have 2 (well clumps really that started as 2 tubers) and the one is about 3 feet high at bloom and the other 5 feet.

However, in general, I'd say that seedgrown cannas would have genetic variations. They mnight all get a bit bigger next year than they were this year, but the general patterns would probably hold true, i.e if Canna 1 is half the height of Canna 2, then next year they'll be the same even if both taller.