Certainly if you want to have one-stop shopping or one person who can tell you about the disbursment of public funds, Treasury Board Secretariat is obviously responsible for that within government. One caveat there is the extent of detail that you would want to go into. If you are really trying to drill down to the project level, you may well find that you may need somebody from the Department of Transport or someone from another department. If you want to have one person, that's fine, but there is a bit of a trade-off there in the detail that you're going to get.
In terms of the broader implementation of the budget, certainly the Minister of Finance is the person who tables the budget. If you're interested in the broad underpinnings of the budget, how it's being reported, and what the accountability mechanisms are, I would have no hesitation in volunteering my colleague from the Department of Finance, or whoever they wish to choose.
The role of PCO, as you know, is partly to ensure coordination across government, partly to provide policy advice to the Prime Minister, and partly to help manage the cabinet committee system. If you want to understand this at a very high level, then certainly PCO, since we perform that function for the Prime Minister, can be helpful, but as soon as you begin getting down to why the Budget Implementation Act says something or other or what the details of a specific program are, it would have to be handed over to my colleagues at the finance department or Treasury Board or another department.