I've been working on canons with my intermediate students. Most players are no doubt familiar with songs like Row, Row, Row Your Boat, or Frère Jacques. Canons are simply instrumental forms of these kinds of tunes that can be played in staggered turns and repeated as you desire.
I like Russian Lullaby because it's in the key of C (easy, no sharps or flats!), and most of the phrases are just ascending or descending snippets of the C major scale. (Here's a handy cheat sheet, showing left hand fingering positions for the C scale. It's from The Ukulele Way, which you really should check out, btw.)
Grab a friend (or two, or three) and give Russian Lullaby a spin. Here are a couple of ways to play the canon. I'm sure you'll come up with more!
Play the entire piece in unison (all together)
Assign parts (Player 1, Player 2, etc.) Player 1 starts, then Player 2 starts at the beginning when Player 1 gets to roman numeral II, Player 3 when Player 1 gets to numeral III, and so on.
Start together, with Player 1 at roman numeral I, Player 2 at II, etc. Play through several times.
You'll be amazed at the lovely harmonies that emerge when the phrases begin to overlap each other. And don't be surprised if what looks like a simple tune turns out to be more of a challenge than you thought. Learning to play your own part while listening to others are playing entirely different notes will take some getting used to. But it's totally worth it, especially if you want to learn to play ensemble arrangements. Uke on and have fun!