If the Canadian government requests the United States government to detain someone, the US would. That's the nature of extradition treaties. Nobody is doing anyone's "bidding".
Sure but don't act like it's just some run-of-the-mill legal process without significant political implications for Canada and their citizens, which are most certainly balanced and considered beforehand. I doubt it's an automatic process merely because a treaty exists.
You're right! It's by no means some run-of-the-mill legal process without significant political implications.
It's a run-of-the-mill legal process that the Chinese government has decided should have significant political implications for Canada and Canadian citizens. It's important to bear in mind that this was a set of decisions deliberately chosen by the government of China in response to Canada obeying its obligations clearly laid out in a readily available treaty.
As you so wisely and correctly note, no legal process is automatic. Yet routine extraditions, even of politically sensitive people, come quite close.
A treaty means it's a matter of law in both countries. It may not be automatic, but if they don't follow the laws they promised to uphold, they risk voiding the treaty.