Nobody says it like this. At least not these days. I have never heard anyone use "hvis" in any such situation (og jeg er norsk).
Do people actually still use 'hvis' like this?
I'm curious because I never hear or see it written these days.
What is the modern way?
I would say: 'hvem sin mat er det vi spiser?'.
Would a construction like "Hvem er det maten til vi spiser?", in analogue to "Hvis sønn er han -- Hvem er det sønnen til?"?
You would rather say "Hvem er det som har laget maten vi spiser" = "Who is it that has made the food we are eating" or "Hvem eier maten vi spiser" = "Who owns the food we are eating". Yours doesn't sound correct...