People from Trois–Rivières/Three Rivers, Quebec are known as Trifluviens/Trifluvians.

People from the recently-created municipality of Three Rivers, Prince Edward Island, are known as residents of Three Rivers.

I don’t think any of the three rivers (Cardigan, Brudenell and Montague) that make up Three Rivers count as fleuves rather than rivières, but it sure would be fun to add Trifluvians to our Island lingo. Let’s do it!

(I came to all this through a 1964 article about Quebec singer Pauline Julien declining an invitation to perform for Queen Elizabeth II during her visit to PEI in October 1964 to mark the centenary of the Charlottetown Conference. Julien’s Wikipedia entry notes she was born in Trois–Rivières and was “the companion of the poet and Québec provincial MLA Gérald Godin, another Trifluvian and sovereignist.” Julien and Godin were both arrested and held for eight days during the 1970 October Crisis, then released without charge. I don’t know if her refusal to sing for QEII had anything to do with her arrest under the War Measures Act, but I doubt it helped.)