Why would we choose to sign up?
There are different reasons and benefits every nation would receive. I will outline these on a country by country basis.
Canadians often share a difficult relationship with their numbers to the south. Fiercely independent Canada has done its best to preserve its national sovereignty. However with a population of only 30 million Canada has seen its place slide over the past decade. The smallest of the G7 economies Canada is struggling with maintaining its military and foreign policy.
Canada is a large producer of oil and other resources however it is part of NAFTA and most Canadians feel aggrieved by the treatment they receive at the hands of the USA when it comes to trade. As part of CINS trade bargaining would be done at super national level giving much more economic weight to deal with other countries and make sure foreign markets are open to us.
Canada also has the issue of its northern boarder. With the North West passage opening up and the scramble for arctic resources Canada needs a much larger military presence to deal with Russian incursion. Canada's traditional Allie America is also scrambling for these resources. Canada may become marginalised as the US and Russia negotiate who gets what in the 21st century.
With a massive resource boom all looks well for Australia at the moment. However present success covers some of the structural weaknesses apparent in the Australian economy. Primary resource extraction is not always going to be so profitable. The economy needs to diversify away from this sector.
Attempts to increase Australias military standing in the region have also met with difficulty. Australia is attempting to build a much larger and more capable Navy however with little expertise in construction of warships and submarines the country is struggling to build these new units.
Australia is also located in a dangerous region. Many of its numbers eye it resource riches with envy. Indonesia is very near by. Not only is it unstable but it has a population 10 times that of Australia. China to is becoming more assertive in the south china sea and pacific areas that Australia considers are in its sphere of influence.
Australia has also suffered from a volatile currency which can often damage its export industry.
In recent year New Zealand has struggled economically. The Kiwi dollar has risen and fallen sharply. This has caused major damage to New Zealand's exports. Its farmers have also suffered greatly in trade negotiations with tariffs imposed against New Zealand.
Incursions in particularly by France during the rainbow warrior incident have highlighted New Zealand's lack of security. With a small military NZ relies principally on Australia and the USA for its security. However in the power plays of the 21st centuary who can be sure that these partners will be their in force at all times.
The UK continues to struggle with its place in the world. With its place in Europe increasingly marginalised by France and Germany as they move closer to integration and its relations with the USA becoming strained the UK desperately needs a new direction. Sustaining its number 2 military power status has become increasingly difficult given the rise of china and the UK's relatively small economy.
The pound has been open to pressure in international markets being attacked by speculators on several occasions. Moving into the Euro is an increasingly unlikely event for the UK. The UK also has to contribute a very large amount of money to the EU over £20 billion per year. With a small agriculture base and a comparatively small export trade with Europe the UK gains little from EU membership.
In short a loose conglomaration of independent nation states dealing principally with foreign policy and monetary policy makes sense for all of these countries.
How to start?
Starting a project like this is not with out precedence. Who would have thought in 1945 that France and Germany would be signing the treaty of Rome just 10 years later. Reconciling four countries which are for all intense in purposes identical would be far easier.
Most voters are not concerned by issues such as trade negotiations, foreign policy and military matters. The first thing to start with should be these areas.
Starting with a common command and control the process could then be rolled out to common procurement and eventually joint deployments. All these military served under a common banner just 60 years ago and have operated together in many numerous theatres together since.
The UK would likely have to renegotiate its position with in Europe. As Canada would have to renegotiate its position with in NAFTA. However with the worlds second largest economy behind them it should be possible to maintain equitable free trade agreements with everyone required.
Foreign Policy could be decided upon by a council of ministers in the way the EU use to be. A single seat on the UN security council would represent all parties and a presidency could be rotated between all the PM's of each country. Becoming the worlds second most powerful man is likely to be quite appealing to the PM's of all countries involved even if its just for 6 months.
In order to build a nation it is necessary to give its citizens something to make them proud. A CINS space program including manned flights possibly even to the moon as well as deep space probes could achieve this for a relatively small cost.
Freedom of Movement
Giving the people of all 4 nations freedom of movement in each others countries would come up against little difficulty. It would probably also be met with wide spread support of the people. Indeed most people cant understand why we don't have it in the first place. Eventually common passports could be issued but only once people are comfortable with the integration process.
One of the key benefits especially for Australia would be a combined immigration policy. Asylum seekers could be spread across all four nations taking much of the heat of of Australia.
After a number of years perhaps 10 or more a common currency should be established. This would give the biggest economic benefits to most of the states.
It would be relativley simple to combine the interest rates of Canada and the UK however much more difficult to factor in the higher inflationary economies of Australia and New Zealand. It would likely be necessary in the beginning to use taxes rather than interest rates to control local inflation. There must also be some form of transfer mechanism between nations who are performing well and nations who are not. A lack of such a mechanism is what has lead to the difficulties being face by the Eurozone at present.
All nations would keep their sports teams in the way that Scotland and England do at present. However a joint Olympic team would help to foster closer national ties. Especially if the team won the Olympics.