Thanks, Zoii, I never realized these 16 nations including Belize (which actually has a sizeable Spanish speaking population) and Jamaica kept the Queen. Well, that would be interesting to have free movement although its a bit of an odd grouping. Now that I know the list includes countries with some diversity of peoples and climates, I like the idea more ... of course, we might want to add some caveats that often come with free movement, as the EU, Mercosur or Australia and New Zealand do (perhaps requiring criminal background checks and limiting access to welfare until one goes through a process of working and becoming a permanent resident). To address Botti's point pragmatically, these are not large countries (population wise) excepting perhaps Papua New Guinea, so even if many choose to come here, it would not be a huge influx of people to Canada. And it would be a great opportunity for Canadians - who wouldn't then need to flock to Victoria to escape the snow.
I don't see anything wrong with the four having free movement as there are some commonalities that make sense, as well as probably political support for the idea. And it would be great to see Canada broaden our horizons. But I am not thrilled with limiting to that list for a few reasons. First, it starts to read like a list of white colonial nations and their UK master. Even though all of these societies are becoming more diverse, such an agreement seems to take us back to the pre-1964 days when the UK and the US were "preferred" sources of immigration (so long as the Americans in question were white). By opening it up more broadly we could avoid that. It also completely ignores French Canada - why not free movement with France? Or other Francophone nations?
Secondly, while from a purely lifestyle point of view it makes sense to choose English speaking nations (ease of movement for workers who can work in their own language), and it opens up different climates, it doesn't do a lot to broaden our horizons by going to these countries. It would be far more interesting culturally for me to spend time in, say Latin America or Asia. It may also enrich our own culture more.
Third, I think there's the question of why we would ignore the elephant in the room (the U.S.) I know, I know - we don't want to be overwhelmed by a country that is 9 times our population, so similar (for Anglophones) yet different politically. At the same time there are so many natural connections, established through hundreds of years of cross border movements and commerce - whether the French Canadian heritage of many New Englanders, or the vibrant ethnic communities in New York, Montreal and Toronto, or the influences of Jazz music. Now, I wouldn't argue for free movement per se, but if we are discussing it with other nations, let's look at our NAFTA relationship, not just our relationship with the remnants of the Empire. (I know there are many family connections among UK, Australia and Canada as well - immigrants from the UK to Canada, as well as immigrants from all over the world to Canada or Australia). It seems odd to me if we'd suddenly see an influx of Aussies, Pohms and Kiwis in BC, while it still remains rare to meet a Washingtonian, and while seasonal workers from Mexico or Guyana have no path to settle here.
Finally, while the common language, and even level of economic development are relevant, we may want to tread lightly on the importance of the Queen to all of this and focus more on what binds our nations - as perhaps close to half of Canadians (including most Quebecois) and a majority of Australians do not support the monarchy.
Let's not also forget that these 4 countries, and several others, already have working holiday programs with Canada.