In Japan, Canon sells the "Pixus" line of inkjets that looks the same
on the outside as their American versions.  For instance, the Pixus
iP3100 looks like the iP3000, while the iP4100 looks like the iP4000.

Of course, the 7-series ink is not even available here, but I was just
wondering anyway.  Are the cartridges interchangeable between the
siblings?

Thanks.