I'd mispronounce
Cian as
Cyan (like the color), but certainly not
Sean.
Kian would be my second guess, just b/c I'm used to a soft c preceding an i or y. (circle, cilia, cycle, etc.)
“The longer I live, the more convincing proofs I see of this truth, that God governs in the affairs of men. And if a sparrow cannot fall to the ground without His notice, is it probable that an empire can rise without his aid?”
–
Benjamin Franklin