Yeah, with the huge popularity of teaching English in Japan and the recent poor economic situation and market saturation, you'd better have a doctorate in English literature, a TEFL certificate and a few years of experience. Then if you are lucky and willing to pay some bribes to the school you apply to, you may have a chance.
Now, seriously, most English teacher don't have any qualification. The only 2 requirement are :
1) to be a native speaker, which means coming from a country which has English as official language, no matter what really is your mother tongue (so if you are a French speaking Canadian, just say you first language is English).
2) To get a working visa you need a 4-year degree in anything. So maths is fine to teach English. Now what if you haven't finished your studies or don't have such a degree ?
As a Canadian you can apply for a working holiday visa if you are between 18 and 30 years old. It's valid for only 1 year (normally non-extendable) and you are theoretically limited to 28h of work a week. Australians, New Zealanders, Koreans, British, Germans and French can also apply for this visa.
You can also get a cultural visa by taking lesson in something realted to Japanese culture, like ikebana or aikido. You can work up to 20h/week with this visa.