Previously posted info is correct. 457mm (18") barrel is restricted.
The guys Fulton are pretty receptive to the idea of getting in to the Canadian market though, so they may be interested in doing a Non Restricted version for us if the interest is there. Criterion is making 476mm (18.75") M1 carbine barrels already so there is definite potential to make it happen.
With that said, I am very interested in the M1 Carbine on a personal level... The fact is I was named after David Marshall Williams. My Dad served in the US Navy and was very found of the little carbine and as far as I remember, it was the first semi-auto long gun I ever fired.