Its likely you have no real fealty to Canadian legal system and govt...and thus it will likely be big waste of time entering any kind of discussion...but let me tell you my basic position anyway:
Canada has every right to have extradition treaty with any country it wants to. Same goes for any other country (incl China). If China arrests Canadian citizen in China because of its extradition treaty with a 3rd party...I would say same thing.
There is no "line of thinking" here. All that has happened is exactly what is stipulated by Canadian law. If you have a problem with that, you can make your case to the Canadian people so they elect people to change that (yes extradition treaties can be ended). There is a process here, and there should be no exceptions based on "feelings".
If you are a naturalized Canadian citizen, you should look up that oath you took again. Read and understand every single word....it matters.
That is for court of law to find and argue (on top of any existing evidence prosecution has to offer). But that only comes later, not right now.
If you would like China to follow a "evidence first, arrest after" policy (instead of probable cause) when it comes to law enforcement....be my guest....it can be the first country in world to do so. It can also choose to violate any extradition treaty it has signed with another country if it pleases as well. Regardless, you should make your case for China to do this all first (for its own country) before requesting it of another.