Is it fine to cancel class on days before national holidays, due to low attendance?
I have known a number of professors who took a third approach: on an expected low-attendance class day such as the day before Thanksgiving, they held a lecture, but did not make it part of the "standard" curriculum.  Instead, they would schedule some sort of fun and exciting "bonus material," like a notable guest speaker or a cool demonstration.  That way, those students who showed up got something out of coming, but the ones whose plans prevented them from being there didn't have any missed "core" material to make up.