Ms. Meng has a proper reason for being arrested (the allegations are that she committed fraud to bypass US sanctions against Iran and sell them US tech by lying about HuaWei and SkyComs involvement to HSBC). There will be a trial, this investigation has been happening for years, and it is by the Justice Department, not a request from Trump (who seems to have been caught surprised by the move). Canada didn't do anything, they are simply honoring their extradition treaties.
In contrast, China is just throwing a fit in response and arresting random Canadians on trumped up charges. These are clearly politically motivated (China had threatened Canada with 'consequences' -- the timing is way too suspect here). We have been given no reason why they have been detained, and there are no court hearings or anything -- they have just been 'disappeared'. With this move, China has shown how authoritarian and anti business they are. No justice department, no investigation. These are simply political hostages. Further more, it is completely spineless that they are going after the, less powerful, Canadian nationals, and not Americans.