~ものだ is a set phrase, meaning "it's natural/obvious/reasonable that ~", i.e., this expression has a nuance of "as a common sense/generally speaking". It's not limited to potential forms. ~ものですかね is a question version, something like "Is it reasonable (to think) that we can enter~". In your example, it could be a rhetorical question "I don't think it's reasonable we can enter~".