The spending authority that's proposed to Parliament through main estimates is based on the decisions that a Treasury Board has taken. The government that is in power at the time that appropriations are sought must take a decision on the nature and substance of the estimates. It needs to balance its own plans against the need for spending authority to continue the core operations of the government. So the government of the day, on any given day, is fully capable of taking the decision of what estimates to present. As you see here in terms of the process, it takes quite a bit of time to put together the estimates. Changes can be made near the end of the process. The President of the Treasury Board and the cabinet of the day choose what estimates to put in front of Parliament.
On May 11th, 2006. See this statement in context.