It's surely not any different than a squirrel, ground hog, or wild rabbit. People eat those all the time. Even meat rabbits seem comparable in size to a guinea pig. You can also just put them in a stew.

Also, as I mentioned, larger animals are also more difficult because you can't just kill one for dinner. If you kill a deer, you have to process it to preserve it or share it with a larger community. Ain't no freezers.

Side anecdote: My grandfather, as a 9 year old, used to go squirrel hunting and bring them home for his mom to cook. Before you go thinking this is some redneck thing, it was long island, less than 50 miles from Manhattan. It would have been during the war though.