A common feature in other Westminster jurisdictions is that the salaries of ministers have to be authorized by law. In the U.K., there are opportunities for two-tier ministries. In fact, currently there are about 21 ministers and up to 100 ministers of state and parliamentary under secretaries.
The flexibility exists for two-tier, but the option also exists to have just one tier, and that's the structure in Canada. Every prime minister, as the minister noted, has the responsibility to structure the cabinet in a way that responds to citizens' needs.