In terms of the committees' approach, you will always be asked about the topic of your study, your mandate, why is it important and in the public interest to have and report that information, in order to be able to hold the government to account.
Then, there may be questions about the reasons put forward. Either the government, or a private company or an individual may have good and acceptable reasons to justify confidentiality. However, sometimes, there are also options. For example, one option could be to require that the information be seen by parliamentarians in camera, or that it would not be explicitly mentioned in a report, but that parliamentarians could have access to it.
For the Afghan files, a committee was set up. People had the security clearance and there were arbiters.
So there are options, and my advice has always been that those considerations not be overlooked when they are reflected in the legislation or when they are in the public interest, because that is important. However, the House has the final word in terms of its procedures, just as courts have the final word when members of the public come before them.