There are a number of cultivars that grow in excess of 6 feet. Catalogers tend to list the heights that are more attractive to the general public. Cultivars such as C. 'Intrigue', C. 'Richard Wallace' and C. 'King Humbert' come to mind. Canna planting that are not regularly thinned or grow in semi shaded areas will typically grow much taller.
From your description, your cultivar is likely related to a primary (specie like) hybrid. You might do a search for Canna compacta, sometimes sold as C. 'Robert Kemp'. This particular plant does produce seed and being a species it produces genetically true seedlings. It can grow between 2 and 2 1\2 meters (6 to 9ft.).
With a good series of photos we might make a rational guess.

Regards,
Kent

Thanks again Kent. That's all I needed to know. I've just gathered some seeds to see if they will germinate. I really hope they do as it would offer me some insurance against losing them all to a virus. My family has been keeping these specific plants alive for over 3 decades.

Could it be canna musafolia? (I've also seen "musifolia" as the spelling, don't know which is correct.) This literally means "banana-leafed canna."

They get very tall, with small red flowers with narrow petals, what some growers call "orchid type" flowers. The blossoms look delicate compared to the leaves. Try a web search for this botanical name and see if the pictures look like what you have. I've been drooling over B&B's summer '12 catalog and saw a photo there. Was thinking about buying this one, actually.

Edie

Edie-I sent you an e-mail, I`ve tons of the banana canna.

Welcome to the south, a LOT of canna get over 6` here.
Tally HO!

It could be plain old canna indica. I grew these from seed, they're fertile. Bloomed the first year from seed.

Eddie_h, what is the B&B catalog? TIA!

Princeton Nurseries: B&B's Plant List