Canada here. Nothing to do with the BCU.
Here when paddling ( ocean ) we try to have a guide on the water first,
another helps with spray decks and launches then he / she follows.
First on the water is a guide and last on the water is a guide. Guide
instructor I am using ad interchangable.
When I have a small group I stick them all on the water , tell them to
hanfg around the wharf, scream and blow whistles when they don't . I
follow as the last person is shoved off the beach by me.
This is for small groups; six and less.

I doubt if BCU or CRCA ( Canadian Recreational Canoe Association ) has
a standard and if they did there are always mitigating circomstances.
This I think would be a judgement thing.
Have a good one Poutine.
Alex