That's a very tricky question. I would have to do a legal opinion and think long and hard about the answer.
I would note that if you're going to pick steel, you should be cautious. For example, in Alberta, if you were going to be looking at upstream emissions in certain other products, you might find they're higher on the domestic level than on the foreign level. I would be very careful in entering the realm of emissions.
To the extent that you picked a lower emission, you would have a better chance of getting it through than you would by picking one that looks highly discriminatory, such as the European Union attempted to do on Alberta oil sands bitumen through its field standard. That caused it to be defeated, because the number was discriminatory and inaccurate.