A general rule in month to month (aka holdover) tenancies is that they can be terminated by the landlord with appropriate notice. Keep that in mind when you're complaining to him about showing the unit. Review the language in your lease. I suspect that it provides that you become a holdover tenant by default if you don't sign a new lease and if you don't vacate at the end of the lease term. I don't suspect that it guarantees you the right to stay on a month to month basis until you decide to leave.
Put yourself in the landlord's shoes for a moment. That unit is a business asset that must produce income. He can't afford to sit and wait until it suddenly becomes available to shop it around.