What does the arrest of Huawei CFO Meng Wanzhou mean for the US and Canada if she isn't released?

I had a few questions regarding her arrest. What could China do if she isn't released? I saw that China has banned iPhones today, could this start a war between The US/Canada and China? Will this just be a "Technology Cold War?" China says there will be major consequences if she isn't released… What could these consequences be?

The consequences will be US companies ending investment in China.

This is really for the best.

China sells nothing we can't produce domestically or buy elsewhere.

Probably nothing.

We're China's customers. They can't afford this. If they get in either a tariff war or a tech war they lose. What they are good at is copying tech. They don't actually make much of it themselves.

What stops China from arresting US citizens?