A big NO from me too.
I don't even see what we would gain out of that.
We should focus on free trade and free movement of people and ideas. North America does not need to be one country to achieve that.
And let's not underestimate the difference between the history, culture and political views of these 3 countries. For the 2 smaller and less powerful ones (Mexico and Canada), unification would mean loosing the possibility to have and express their own ideas on politics, economics, society, etc,... (however small, even very small, it could be right now).
And for the USA, I think they have enough problems like that, without having to deal with the Canadian and Mexican ones.