They have NO RIGHT to be asking all the questions. FULL STOP. If they were "working to rule", here are the rules. Quote these next time, and if they continue to hassle you, ask for a supervisor.

From:
CIC Document ENF 4 -- Port of Entry Examinations
8.8. Basic questioning
Basic questioning should cover the following areas, as appropriate:
Issue Question Explanation
Identity What is your name? This will enable an officer to identify the person. The name should be verified against the referral card, identity documents and the airline ticket.
Citizenship Of what country are you a citizen?
The officer should ask this of each person being examined and ensure that the person's stated citizenship matches the identity document they present.
This response will help an officer determine passport and visa requirements. If satisfied that the person is a Canadian citizen, the officer should allow the person to enter Canada without further questioning.

AND FURTHER...

9.1. The right to come into Canada
A Canadian citizen within the meaning of sections 3 and 4 of the Citizenship Act has a right to enter and remain in Canada pursuant to section A19(1) of the Immigration and Refugee Protection Act.
9.2. Examination of Canadian citizens
Subsection A15(1) provides for an officer to proceed with an examination where a person makes an application to the officer in accordance with the Act.
Subsection R28(b) provides that a person seeking to enter Canada is making an application.
Additionally, A18(1) requires every person seeking to enter Canada to appear for an examination to determine whether they have the right to enter Canada or may be authorized to enter and remain in Canada. This includes Canadian citizens.
An immigration officer will normally examine a Canadian citizen only when the PIL officer doubts the person’s citizenship. An officer at a port of entry should examine Canadian citizens as expeditiously as possible. Once an officer establishes that a person is a Canadian, the examination should end and the person should be allowed to enter Canada without further delay.
It is not appropriate for officers to elicit further personal information from a Canadian citizen.
Canadian citizens may be asked to willingly provide additional information if it will assist an officer in determining the admissibility of an accompanying foreign national.