The UK will never be in a free trade bloc with the USA and Canada already has a free trade treaty with the USA. If the CEA comes into being then there is no reason why the UK cannot agree a free trade deal with the European Common Market in addition to being the engine of the CEA.
Not so certain USA and Canada are in a free-trade zone
I would of course like Britain to be in both zones. However it is not always so certain if se can get everything we want. I'm just airing some possible difficulities, for all we know EEC won't accept us if we're planning a Commonwealth Economical Area. And they can accept us even if we are a part of it.
But if we could only choose one, which would you like? And I never expected you guys to actually take my idea of a Commonwealth Union serious ^-^