The Shorts Belfast sells widely; France, Canada, Australia, South Africa, India and Brazil all have niche strategic airlift capability by the mid 70s.
Interesting idea, but a lot here depends on how many they buy. If these countries all buy similar numbers to their OTL airlift fleets, this means about 15 aircraft for Canada and Australia, 10 for South Africa, 50-60 for India (most probably built by HAL), 20 for France and 10 for Brazil. The big question with these is what they get used for. Are they there early enough to back up the Australian Army in Vietnam? Do the South Africans use them for paratrooper or support operations like they used their Transalls? French use them in Africa? Gulf War? Canada backing up General Dallaire's forces in Rwanda in 1994?
US Army agrees to standardise their rifles with NATO, getting the Belgian designed FN FAL instead of the M14 or later the M16. This eventually extends to all US armed forces. The AR-15 remains a Special Forces only weapon.
Why bother with this one? The FAL and M14 use the same round, and the FAL was phased out by many of its first-world users as the M16 was being brought in. The AR-15 series as a special forces only weapon raises the question - what does the US replace the M14 (or hypothetical FAL) with in the 1970s?
US Navy buys the T-45B Goshawk for land based training roles. These are a lead-in to the T-45A ship based trainer aircraft.
RNZAF gets the F-16 order they wanted in 2001.
The question on both of these is why? The Goshawk isn't supersonic, whereas the T-38 Talon is. Better to buy a supersonic trainer like the Alenia M-346 or KAI T-50. F-16s for the RNZAF is another why question simply because of the fact that New Zealand is so far away from anywhere, has no real external threats and rarely sends troops abroad in any real numbers.
Britain buys the Hawker P.1123 to fill the role the Phantom did in OTL. And instead of TSR.2 goes for a joint project with France based on the Mirage IV, also the Vickers V.1000/VC-7 is bought as a tanker/transport by the RAF helping to justify the launch of the subsequently highly succesful airliner version
The P.1123 is an interceptor, so the Phantom would be a better multi-role aircraft. I think the idea of a Britain-Canada-Australia fighter purchase can get more done, with the Phantoms assembled in their respective countries with components from all three countries, with RR Spey engines and Commonwealth electronics. The Vickers V.1000 is an obvious what if. The TSR.2, if anything, would probably work better in reverse, as the Mirage IV has a bigger payload but shorter range and less sophisticated electronics. I'm thinking a TSR.2 with SNECMA turbofan power and its high-end electronics for both the RAF and French Air Force.
Canada buys the F-4 instead of the F-104.
See above. Spey-powered Phantoms with Commonwealth components made by Canadair would be a wonderful improvement to the RCAF in the mid-1960s and later.
Canada buys the A-4 instead of the F-5.
At the timeframe the F-5 was bought (late 1960s), if Canada is buying attack aircraft the A-4 would be a cheap buy but not the best one, the best one would probably be the A-7 Corsair II, which if Canada has the Phantoms above would allow engine commonality, as the Allison TF41 from the A-7 is effectively a license-built Spey.
Canada buys the F-15 instead of the F-18.
Why the Eagle? It has no ground-to-air armament. If Canada has the $$$ for a dedicated interceptor in the 1970s, the Tomcat would probably be better for its greater range and the Phoenix missiles. If you want multirole aircraft, the Hornet is superior until the Strike Eagle comes around in the early 1990s.
Canada replaces the CF-5 with either the F-16 or the F-20 rather than not at all.
F-16 would be a major increase in capability over the CF-5, but F-20 would be a waste of time in a bunch of respects, namely range and payload. Considering Canada would assuming all of your suggestions happen have a fleet of F-14, F/A-18 and A-7 aircraft already, having F-16s or F-20s added to the fleet is a bit pointless.
Canada purchases the Chieftain or Challenger II instead of the Leopard C1.
Why call this one off? The Chieftain would be no real improvement on the Leo 1 (aside from the 120mm gun) and the Challenger 2 isn't available yet.
The EH-101 purchase is not cancelled.
Considering all of the crap that the Cyclones have given us, I'm kinda inclined to agree on this one, though as always I'd prefer something made in Canada rather than abroad.
Canada purchases either the Rubis-class or Trafalgar-class nuclear submarines.
The Trafalgar or Rubis (particularly the former) would be a HUGE step-up in capability but at a major cost. The 1987 White Paper called for 10-12 such submarines to be bought or built in Canada, which would be if done a project that would extend right through the 1990s but would give Canada a capability that few nations other than the US, Russia and UK have.
Canada and the Netherlands stay in the Tornado consortium.
If Canada stays in this in the early 1980s it would have to be a multi-role aircraft and not strictly an attack aircraft, or Canada would have to be confident enough in the Tornado and have sufficient funds to buy an interceptor aircraft in the 1970s to replace the CF-101 and F-104 (or the Avro Arrow if its built) and also to buy a fleet of the Tornado. For the Netherlands, they would have to butterfly their NF-5s or have sufficient funds to replace the F-104 with the Tornado rather than relying on the F-16, which is possible but not easy I suspect.
Sweden, Spain, and Australia buy the Apache like they originally wanted to.
Australia would probably have loved to have the Apaches in Afghanistan and/or Iraq, I'm sure of that much. Not sure why Sweden would buy the AH-64, though.
The Westland-Sikorsky consortium doesn't fall apart and Britain gets Rolls-Royce powered UH-60's and CH-53's.
RR-powered CH-53s I can see only if the Royal Navy keeps its carriers or the Royal Marines have a bunch of their own dedicated assault ships. Other than that or butterflying the (faster and just as capable) Chinook, there is no point. A Westland Black Hawk might also be good for Canada and Australia, the former of which needs real medium transport helicopters and the latter of which bought Black Hawks in any case.