Canadian law (how to deal with the boss who absconded to Canada in arrears of wages?

China has no jurisdiction over crimes committed in China.

If this person has been convicted in China, he may have concealed his criminal history in China during the Canadian immigration. You can report it to Immigration Canada. If the report is indeed accepted by Canada, it is likely that his immigration application will not be approved. If he has completed immigration, if he conceals his criminal history, he will be held accountable for fraudulent immigration laws. However, litigation in Canada is a very long and expensive process.

If the person is not convicted or wanted in China. Then you can't do anything about him.