I was shocked listening to some kind of canon from the Renaissance. They use polyrhythm extensively.
So I tried... This little canon works this way:
Two parts (8 + 8 measures).
The middle voice and the bottom voice are in 5/4. The middle runs twice faster.
The upper voice is the same than the bottom one but in 7/8.
The gaps when one voice finishes earlier than others (very few gaps, indeed) are in free counterpoint.
I like the result, romantic and impressionistic with mild dissonances.