Do they need full sun?
Are you speaking of cannabis or amarilla?
Because I cannot find anything called cannis on the internet..the one picture I could find looks like an amarilla.
If you tell me which one you are speaking of I can maybe help you out.
Canna or Cannas plants should have full sun but can live with a little less. Mine have always grown at least 6-7 feet. They multiply excessively & bloom in the Fall. (at least here in MN, they do!)
Canna lilies need full sun. So do cannabis plants... I've never heard of Cannis.