I never had to certify my own translations.
On this link: http://www.international.gc.ca/missions/japan-japon/visas/menu-eng.asp
If 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.