Cut off what bits? I f you mean the growth, no, don't cut that. You can pot into larger containers if you want - the size looks fine at the moment, but Canna do get huge (the corm I mean) by the end of a season, by which time they'll probably be distorting those particular pots into an odd shape and will be difficult to extract.

I mean the dead, dried looking bits at the bottom of the leaves which looks like a remnant of last years leaf, maybe seen better on second pic? What feed should I give now?

Well you can cut those dried bits off if you want - won't be long before you wont' notice them anyway though. They do fine in ordinary multi purpose compost - I feed mine with Miracle Gro general purpose once a week from now till end of August.

Thanks Bamboo, should I start letting them out for the day if weather is fine?

Oh yes, certainly. Mine have been out on the balcony all winter - and survived!

Do they like the soil to be quite damp?

Not particularly - let it dry out slightly between waterings, as with most everything else

Thanks Bamboo, I'll leave the bits on if they don't matter:-)