I have just extended my visitor visa and found a job in Canada. Is it possible to apply a work permit from Canada or should I go back to Japan?

You can’t apply a CIC work permit at CPC once your status become visitor. It is, however, not necessary to go back to Japan. You can apply at any Canadian visa office in US.

The most imporant thing is that you have to obtain LMO from HRSDC PRIOR TO the application for the CIC work permit (unless your job is exceptional). This may take upto 1-6 months depends on your region. Montreal seems not too bad, but as you also need a CAQ and collecting documentations are so time consuming, practically, I think you won’t be able to work within 2-3 months.

For more details, (incl those terminologies), check CIC and HRSDC website. Good luck.
　

Thank you very much for the information. It means that it’ll take at least one month after applying the work permit from the U.S, right?
Should I absolutely wait for the permission or are there any possibilities to help the employer until then, such as an internship or a volunteer?
　

I’m not res1, just so you know.

I don’t think you’re getting it right. It doesn’t take time before you work if you have LMO. It takes time to get LMO. And unless your job is exceptional, you need to get LMO. If you have LMO, you can go to the US to get a work permit.(And it doesn’t take one month. You can get your work permit right away.)

If your work place is not a non-profit organization, it’s illegal to work there.

That’s what I learned from this site. Correct me if I’m wrong. 　

Thank you for your comment.
I hope you are right. The problem is I need to be authorized by Quebec gouvernment. That’s tricky.

Does anyone know about the time I can expect in case I apply for my work permit in the U.S?