Stony corals are CITES appendix II. You need to have an export permit to move them from Canada to the US or vice versa. In the US, this is monitored by border patrol (CPB) and the USFWS. For shipments entering the US, you need a form 3-177 with a CITES stamp on it. In Canada, I think it is monitored by Environment Canada.
People saying you can do this and that they have done it are technically smuggling and just didn't get caught.
There is a coral dealer in the Detroit area that has/had a sign saying "All Canadian customers must pay cash in USD". The reason is that they didn't want a paper trail of having sold corals to Canadian citizens. Their parking lot always had a lot of Ontario plates on the cars (grin). USFWS was aware of this, and I think they followed some of these cars and made arrests (that was many years ago, and may just have been a rumor).
Here is a document:
Jay