They are not at the behest of the Treasury Board because the Treasury Board is a committee, not an administration or agency. The board has no executive authority whatsoever and exists to give advice to Cabinet rather than to perform or execute a duty. However, the individual members of the Treasury Board do have the ability to order the CRA, principally the Minister of National Revenue, who sits on the Treasury Board, is the executive of the CRA.
Perhaps you're thinking of the Bank of Canada, which is an actual corporation and operates in a semi-independent manner from Parliament, although technically Parliament has full oversight and authority over it.