Oh "critters" is totally American--but I'm pretty sure it dates back to almost Elizabethan times, when settlers from England wandered off up into the hills and kept talking that way long after the language of folks closer to the seaports evolved. If an American uses either "victuals" or "breeches" at all today, s/he is likely to pronunce them as spelled, just as s/he is likely to say "creatures".

Linguistically, the vittles/britches/critters pronunciation must be related. Wonder why they fragmented...?