The MOU says it can be cancelled, but the law says it can't, as I understand it. I'll get to my point here.
Paragraph 15 of the MOU reads:
Prior to each fiscal year, the Director will consult with any individuals or entities, including the RCMP, the House of Commons, the Senate, the Library of Parliament, to ascertain security requirements, including planned or anticipated events for the Parliamentary precinct and the grounds of Parliament Hill and will prepare a draft estimate, for the approval of both Speakers, of the sums that will be required to pay the charges and expenses relating to the Parliamentary Protective Service during the fiscal year.