In 2020 the net worth of all Arasaka assets is aroung 500 billion e$. That's roughly the economy of medium size country like Canada
Well, this is wrongo. Canada's GDP is 1.73 trillion. Yes, trillion with a T. We are the 10th largest GDP in the world. We are, frankly, an economic powerhouse. Our natural resources are valued at 33 trillion, fourth in the world. An "energy superpower" to quote Wikipedia.
As for Arasaka's valuation at 475 billion, a couple things have to be noted: the Corpbook that comes from was written in 1990, and is valued to 1990 dollars estimate for 2020. In the late 80s, IBM was worth about $20 per share and was absolutely a megacorporation.
Today, in late 2019, there shares are worth $140/share. And IBM is no Apple or Google - they are a fairly blue-chip, steady-growth company. 700% growth over 30 years.
Using that multiplier for Arasaka, they would be worth not 500 billion dollars but 3.5 trillion dollars in terms of being a powerful megacorp if R. Talsorian wrote them today. In other words, staggering wealth. Which is what R.Tal wanted you to think when you read 475 BILLION dollars in 1990.
Secondly, and what I impress on all my players, is that a lot of the stuff in those Corpbooks is subject to error. Merrill Asukaga and Finch don't know everything. As the book says, "Remember, our suggestions are just that...suggestions!".
You want to impress on players not that Arasaka is worth 500 billion, but that they are staggeringly wealthy - Google Plus scale. That's the point of the Corpbooks and the data therein.
As for the size of Arasaka's army, the original topic, well.
Walmart today employs 2.1 million people. McDonald's 1.9 million. Assume Arasaka by 2077 is -the- Security company by 2077 (debatable) and the population has recovered to our current levels (also debatable) that means 2 million people.
How many are soldiers/guards? Well, good question. The US Army (just the Army, mind you, not the NG or Reserve) has some 460,000 members or so. 15% of those are infantry. Let's assume Arasaka, being efficient, double the amount of their personnel that serve as combat arms. But, wait, Arasaka is spread out allll over the world, means transport, logistics, commo, etc. Much much more so than even the US Army. AND Arasaka has a very powerful banking and service sector.
So, say 20% of Arasaka employees are Combat Arms. That's 400,000 armed troops in 2077. Still huge, but not..millions.
And it's just as possible they'd keep their troops at 100,000 or so and use, say, drones and electronic security.