I think Fujica cameras used m42 mount?

m42 and Olympus OM mount, both would work on Canon DSLRs.

Just about anything can be adapted to mirrorless bodies.

The question of DLSR vs mirrorless is largely a question of what ergonomics you prefer, you could pick up a cheap adapter for your T3 and let him try it out, https://www.amazon.com/Fotodiox-Lens-Mount-Adapter-Olympus/dp/B001G4NBNC