Suzuki Samurai rear diffs are pretty compact, as are the rwd trans. Bell housing bolts up to several motors, from the little Metro 3-cylinder to the Swift GTi engine, to the 1.6L out of Trackers.
Suzuki axles out of Carry's have GOT to be small, being used behind 660cc turbo engines. You should be able to find them through an importer or something in Canada...if you really want something small and light...