As well as the tunnel entrance

I get the feeling everything was moved out when the police set up a 2 mile radius quarantine. They will most likely just be cleaning and doing construction while the employees are gone.

I almost never watch videos, but this is standard for "prestige" businesses like CP. They don't want their employees bitching about them and making them look bad. The normie not-a-conspiracy version of this process is someone critical says they're too shaken to come back in immediately. The boss shrugs and decides not to screw with replacing the critical person under such understandable circumstances, and gives everyone else the day off. It's not that hard a decision to make if the operation is more about politics than capitalism. Not saying that's what actually happened, but it's an important possibility to get in the conversation.

Is there some reason a stakeout on a day the place is closed would be especially productive?

Having been through a store robbery (armed) we didn't get the day off. That seemed a bit weird. Granted our store wasn't getting "threats" either.