The Federal duty-free allowance on importation of alcohol from Canada is still 1L. But, I routinely bring 2-3L in and have only been charged duty once in the past few years. I just get waived through. Although the US does not have "transit" as a technical legal matter, the fact that you won't be consuming in the US may also cut in your favor as a matter of the inspector's discretion. I would definitely not omit it.