I am a Canadian citizen residing in the UK and will be travelling to NYC via Toronto. The ESTA website, and other responses I read online here have indicated that you do not need an ESTA in my circumstances. However, the ESTA website notes that you require a valid Canadian passport AND a valid Canadian photo ID (i.e. Ontario Health card, Drivers Licence). I do have a valid Canadian passport but no longer have any other Canadian photographic ID and wonder if I will still be able to enter the US without an ESTA?
Canadian citizens never require an ESTA to enter the United States (CBP FAQ). You will in fact find on the ESTA website, should you nevertheless attempt to apply, that Canada is not listed in the "country of citizenship" field.
Aside from that, Canadian citizens entering by air do require a Canadian passport (US embassy in Ottawa source) or NEXUS card, and Canadian citizens entering by land or sea require either a Canadian passport or another Western Hemisphere Travel Initiative-compliant document, which are basically either an Enhanced Driver's License or a NEXUS/SENTRI/FAST card. You will not need a visa unless you are doing something like getting married or studying abroad, which I assume is not the case.
You do not need more than one document and I am not sure where you saw on the ESTA website that Canadians require more than one, particularly as Canadians don't need to use the ESTA website at all in the first place. As you're already traveling with a Canadian passport from the UK, that will suffice to get you into the US.
According to U.S. Customs and Border Protection, you do not require an ESTA in order to enter the United States.