I am a Canadian citizen who lives in Belgium. I want to visit NY this summer. Do I need a ESTA waiver for that?
Canadian citizens do not need a visa to enter the US (with some exceptions). They do not need a visa waiver, and so do not need an ESTA. Residency is not an issue. You will of course need a Canadian passport to take advantage of this.
The ESTA is only relevant for citizens of Visa Waiver Program countries, which you are not. Like many other such rules, what matters is your citizenship, not where you currently reside or travel from.
I am not sure of the exact rules for Canadian citizens but I think you don't need any visa or prior formalities for a short visit to the US. The Timatic database confirms this.