I'll be taking an Air Canada flight from YEG to LGA (connecting in YYZ). I vaguely remember having taken Canada to USA flights before where immigration/customs was done beforehand in Canada, rather than upon arriving in the USA. However, I've never taken AC.

Does anybody know if this route would do the immigration/customs in YEG or YZZ, or will I have to do it at LGA? I'll be very tight on time and just trying to figure out in which case (if any) these checks are done before departing Canada.

Thanks.