Ask HN: How does tax work on corporation sales?

So I was wondering. You hear about these big $500 million, $1 billion exits, or say something more modest like $5 million, $10 million.

Do you just pay capital gains tax? Or do you just pay income tax?

Or do you pay both? Is it possible that you sell for $10 million and end up with like $6 million due to taxes?

USA and Canadian input would be interesting given that I'm in Canada.

I know people will say things alluding to tax secrets of the wealthy, but can anyone actually elaborate specifically on what actually goes on?