They both mean "sandwich". The word "sande(s)" is commonly used in Portugal but it's not used in Brazil.
Shouldn't there be a will or going to in between we and eat? or is that just portuguese?
This sentence could be interpreted as either the past (were) or the present (are). To be future (which would require will or going to in English) it would have to be written:
- Nós comeremos um sanduíche
- Nós vamos comer um sanduíche