MacNaughton and Brison, the president of the Treasury Board, will round out the contingent along with Mulroney, a close friend of Bush who is scheduled to deliver one of several eulogies during the ceremony.
Federal officials say Prime Minister Justin Trudeau and Mulroney spoke by phone about the eulogy over the weekend.
U.S. President Donald Trump has declared Wednesday a national day of mourning in the U.S., part of a week-long state funeral that began Monday with a public visitation in the Capitol rotunda.
WATCH: Brian Mulroney says passing of George H.W. Bush is ‘a tremendous loss’
Bush will be buried Thursday at his presidential library in Texas, near his wife, Barbara, who died in April, and their daughter Robin, who died of leukaemia at age 3.
An official in Ottawa says Trudeau will announce this morning that flags on all Canadian federal buildings in both Canada and the U.S. will be lowered Wednesday, similar to the tributes that marked the deaths of former presidents Ronald Reagan in 2004 and Gerald Ford in 2006.