우리 쌀 있나 보자.
있나 functions like 있는지 and they can both be used in this context here, but 있나 has a better nuance of speculation. 있는지 is a factual way of saying whether there is (or not) and comes off stiff in this context.
Some other sentences following this grammar pattern could be:
- Shall we check if she’s asleep? – 걔가 자고있나 (한번) 보러 갈까?
- Lets have a look if its hot outside – 바깥 덥나 보자
- Shall we have a look whats on TV? – 티비에 뭐하나 볼까?