The Montreal MP favours limiting senators to 12-year terms but, other than that, sees no need to overhaul the much-maligned chamber.
He rules out the election of senators as a "terrible idea" that would lead to parliamentary gridlock and exacerbate the under-representation of western provinces.
Rather, Trudeau says the obvious fix is to "demand better" of those appointed to the Senate.
He says the recent series of controversies that have befallen the upper chamber are largely the result of bad choices by Prime Minister Stephen Harper in appointing senators.
The Senate's already tarnished reputation has been sullied by allegations of senators abusing their taxpayer-funded housing allowances and by the arrest last week of Conservative Sen. Patrick Brazeau, who was charged with sexual assault and assault.
Brazeau and fellow Harper appointee Mike Duffy are among three senators whose expense claims are being examined by an outside auditor amid allegations that they improperly claimed an allowance meant to compensate senators who keep a secondary residence in Ottawa. The third under investigation is Liberal Mac Harb, who was appointed by former prime minister Jean Chretien.
Trudeau, who won an upset victory over Brazeau in a charity boxing match last year, declined to comment specifically on the controversies swirling around his one-time pugilistic adversary.
But in general, he said recent scandals "are a reflection of an institution that we haven't taken proper care of and that the prime minister has gone out of his way to fill with people who, perhaps, aren't focused on serving Canadians with the best of their ability the way they should be."
"It needs to be fixed by demanding better of the people that we choose to appoint to the Senate. That's the answer for me," he said after a pep talk late Monday to several hundred Liberal supporters at a pub near Ottawa.
Trudeau defended the Senate as a necessary "counterpoint" to the elected House of Commons and praised most senators for doing "extraordinary work."
Harper's government has repeatedly introduced bills to impose a nine-year term limit and promote the creation of provincial processes for electing nominees who would then be appointed to the Senate. After numerous false starts, the government has finally asked the Supreme Court to advise whether such reforms can be implemented by Parliament alone, as the government maintains, or would require a constitutional amendment approved by at least seven provinces with 50 per cent of the population.
The court has also been asked to clarify which constitutional amending formula — seven/50 or unanimity — would be required to abolish the chamber altogether.
Trudeau turned thumbs down on electing senators, without first changing the gross under-representation of western provinces or establishing a deadlock breaking mechanism between two elected parliamentary chambers.
"I think an elected Senate is a terrible idea," he said.
"If you all of sudden have a legitimate Senate that exercises the full extent of its powers — as opposed to one that understands that it's less legitimate than the House of Commons because it's not elected — you're transforming our system in very, very negative ways.
"Not to mention that all of sudden Alberta with only six senators who are elected is much weaker than Quebec, that has 24 senators that would be elected. It would unbalance so many things that we just have to focus on making it a better quality Senate rather than trying to change the Senate."
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