For an even more specific question, were any in office politicians vehemently against the acquisition of Hawaii or the Philippines?
The history books in school do a good job of glossing over the subject, almost making it seem like everyone was in agreement about acquiring overseas territories. I highly doubt some of the more liberty oriented politicians would have approved such actions.
I'd say that several members of the transcendentalism movement, most notably Ralph Waldo Emerson and Thoreau wrote at great length about what we'd now call anti-imperialist sentiment. As far as politicians go, while many were against the war the overall tide of public opinion made opposing the war political suicide. Most objections were made privately.
The US, like most other imperialist powers at this time, was careful to phrase imperialist ventures in terms of liberating oppressed peoples (like the Philippines or Cuba) or in terms of paternalistic governance (think Hawaii). You're right to say there was resentment against this - but it was generally wrapped up in politics far outside the mainstream as of yet, mostly socialist and anarchist circles.
the american anti-imperialist league is exactly what you are looking for.
One interesting tidbit from history is the Teller Amendment.
Fearing annexation by the US, Senator Henry M. Teller of Colorado put forth a bill and passed it that stopped any attempt at annexation of Cuba following the Spanish American War.