Here is another possibility....

You could start off at 1000 cann = 1 gram. Then as buy support increases and as more dispensaries start offering cann, you could go to 500 cann = 1 gram.

Then you could go to 100, 50, 10, 1 etc.

I'm just thinking that this would solve 2 problems:

1. This would obviously solve the problem of cann having so many coins.

2. This would solve the problem of traders dumping the coin because people would want to hold on to their cann for when it goes from 1000 to 500, etc.

You could even have exact dates named where the peg would change.