No, I do not think that the United States, Canada and Mexico should all adopt the same commercial laws and one currency, because the currency in Mexico is not as strong as the currency in the United States and Canada. What little Canada's strong currency would help the United States, Mexico's currency would bring us down.
There would be no reason for the Canada, Mexico, and the United States to unify into one country. There is already enough conflict within each country without inviting more. As an example, Canada has Quebec wanting to secede. There would also be numerous language barriers, with people in Mexico speaking Spanish, people in the US and Canada speaking English and French. And, to make it even more difficult, there would have to be a lot of maneuvering to change the laws and governments to be unified.
I would prefer to keep the currency systems the way they are today because they accurately reflect that individual country. Any type of conglomeration would cause all countries involved to take on extra assets or debts from another country, and could cause widespread problems as inflation or deflation catches up.
The economies of the United States, Canada, and Mexico are very different, as are their currencies. I do not believe we should all adopt the same commercial laws. Each country is unique and different and there is no reason to move in the direction of unity. I think such a change would be a failure.