My in-laws mix both "nopal" and "tuna". Possibly depending on context, but I'm still studying Spanish and nowhere near 'native speaker' level.

I just call them "nopal" as I hear that word more often. Possibly due to the saying "Nopal en la frente" when they tease my sister-in-law her husband.

I can imagine "tuna" being confusing to English-speaking natives :-)