Good question. I would think its possible that it falls under the "anything greater than 20mm" ban from the May OIC, although then the argument could be made (and has been made) that all cannons would also fall under that and I have not heard of anyone getting in trouble for their cannon yet. The government has made no comment on cannons/black powder stuff with respect to the 20mm ban that I am aware of, so its a big question mark currently as far as I am aware.
Maybe contact someone like IRG or Prophet River, they do imports so they might be able to tell you if they could bring it in for you or not?
Does look fun though!