Choose bell peppers that are roughly the same size with relatively flat bottoms so they can stand up right.
It's important to note that depending on the size of your bell peppers, you may end up with extra filling (or not enough). Medium sized peppers are ideal for the amount of filling here. You can always add extra rice to the mix if your peppers end up being too large!
Either brown rice or white rice will work here.
Strained tomatoes typically come in a jar. If you can't seem to find them you can substitute with 15-16 ounces of canned tomato sauce.