What are the major differences (if any) between the air traffic control service in Europe vs. USA vs. Canada?
One of the big differences between regions is how aircraft operators pay for the service. In the US, the FAA is funded by taxpayers and fuel levies. In New Zealand (for example), aircraft operators are billed for use of air traffic control services. I don't know what the billing situation is in Europe.
Very, very few. We (not just the West, but most of the world) all follow ICAO document 4444.