Sounds like you are trying to build a TSCIF, which could be problematic given that it also sounds like you'd like it to be a general-purpose planning room.
I don't know how it is in Canada, but in the US there are very strict rules about controlling access to such a site. I.e., specific locks, windows and doors, manned entry points, etc. No need to say more here, but if classified materials are going to be handled there it is probably not a good location for your sand table. Sand tables are great for briefing missions, especially for the guys who may have lower level clearances.
Consider putting the sensitive materials in a separate room and keep an outer space for all the other activities. Also, you might get a buddy in MI to help you understand what can and cannot be done.