hum... you read my thoughts, because 40% of my family works in Ottawa
I would say with a 100% assurance, you need to be Canadian or need citizenship to work in any government job... is not obligatory but you will face other major preferenes, see this
While the Public Service Employment Act does not exclude non-Canadians from applying to positions in the federal public service, it clearly specifies that preference for appointment is to be given in the following order, among the qualified candidates in a selection process:
1.Canadian who is in receipt of a pension by reason of war service;
2.Canadian war veteran or a survivor (widow/widower) of a Canadian war veteran;
3.Canadian citizen; and
4.Other qualified individuals.
(Canada public servant job data base website)