The giant Mike Duffy-shaped balloon

It's part Goodyear Blimp and part Stay Puft Marshmallow Man, all rolled into one enormously inflatable symbol of Senate excess.

Meet Mike Duffy, in balloon form.

The beleaguered senator from Prince Edward Island was rendered as a two-and-a-half-storey blow-up doll for the Canadian Taxpayers Federation's campaign to hold a referendum on the fate of the upper chamber.

Spokesman Gregory Thomas was clad as a carnival barker, complete with cane and flat-top hat, as the big Duffy balloon lurched to life by the shores of the Ottawa River.

"Step right up, ladies! Step right up, gentlemen!" Thomas shouted. "Come and see the senator who nearly ate a government."

As he spoke, men holding ropes laboured to keep the swaying Duffy doppelganger and its overflowing briefcase of cash from toppling into the water and floating away.

"Two thousand, one hundred and fifty cubic feet of hot air, with a grossly inflated sense of his own self-importance, and a giant bag of taxpayer money," Thomas said, later adding the big balloon cost his group $4,700.

Thomas says Canadian voters ought to have a chance to decide whether the Senate should be reformed or abolished altogether during the next federal election.

"We believe that every Canadian voter should decide the future of the Canadian Senate, not politicians, not judges and certainly not the unelected senators themselves," he said.

Duffy is being investigated by the Mounties over his improperly claimed Senate expenses and for accepting a $90,000 cheque from Prime Minister Stephen Harper's top aide.

Former chief of staff Nigel Wright quit after word leaked that he cut Duffy the cheque to allow him to pay back invalid housing allowance and expense claims.

The senator did not respond to an email asking how he felt about the stunt. He has also been lampooned on Prince Edward Island, where popular "Stuff the Duff" T-shirts depict him being dumped head-first into a trash can.

Duffy is one of four senators whose spending has put them in the hot seat. Pamela Wallin, Mac Harb and Patrick Brazeau are also under the microscope.