I don't know if stuttgart is different for some reason, but this is my second year starting my canna around this time. I bought some from Ebay last year (purpurea) and just potted them up and started them. They did really well last summer!

A few days ago I brought mine back out from storage. I haven't potted them yet. I might just leave them in their box to slowly wake up.

I'm certainly not an expert, but my vote would be pot it up and start it with your banana plants. I don't know if it'll honestly give you a jump on growth when it's all said and done (they all seem to catch up to the same level once they're outside in warm soil), but if you just want to see a little growth I don't think it'll hurt anything either.

Thanks turquoise, I just potted it.