Hi ery,
I never had to certify my own translations.
On this link:
http://www.international.gc.ca/missions/japan-japon/visas/menu-eng.aspIf you look at
Temporary Residents >
Visiting Canada there is a
Guide to apply (a PDF file) which says on Page 3:
If the documents are written in Japanese or any other language, please
provide an English or French translation.
An unofficial translation will suffice. My friend is a freelance translator. I can give you her contact details if you send me a private message, although I won't guarantee that she will do it, mainly because she is very busy. If that's the case, she may be able to recommend you some agencies or translators.
Good luck!