Amnesty, UNICEF, Bill and Linda Gates Foundation, as far as mainstream charities go. I believe they all have specific Canadian divisions if you are worried about tax reasons.

Some others you might check out are Canadian Centre for Policy Alternatives, Canada Without Poverty, Equiterre, Canadian Council For International Cooperation, Tides Canada, CoDevelopment. I had a longer list but misplaced it.

I also strongly suggest you research each charity on your own instead of depending on whether or not a ranking website tells you it is good.