Any North American monetary arrangement would most likely mean that Canada would have to adopt the US currency. For Canada, the other major problem with a single North American currency is that we would be giving up the buffer that a flexible exchange rate provides in dealing with shocks that affect us differently from the United States.
An important contrast between Canada and the United States is the distinctly different impact that fluctuations in the world prices of primary commodities have on our two economies. To a significant degree, Canada is still an important producer of primary commodities. And we are major net exporters of such commodities, while the Americans are small net importers.