It proved the Duchess of Cambridge is fashion conscious and clearly considers each outfit before she deciding to wear it.
But it also shows she knows a little bit about history too as she wore a similar outfit to that of her husband's mother, Princess Diana - who would have been Kate's mother-in-law - when she visited Canada in 1983.
The Duke and Duchess of Cambridge are on a nine-day tour which spans seven cities and five provinces.
As part of their trip the couple will include stops in Alberta, the Northwest Territories and Quebec before jetting off to Los Angeles.
Their tour is much shorter than Prince Charles and Diana's who spent 18 days in the Commonwealth country.
Princess Diana was the main attraction with thousands of people waved flags and shouted the slogan 'We Want Di'.
Prince William's new wife has also been a real crowd pleaser and her wardrobe had been one of the main topics of discussion.
She has a few old favourites among the 30 outfits she has packed for her trip to the U.S. and Canada.
The white dress she chose for a citizenship ceremony in Ottawa was the same one she wore for her official engagement portrait with Prince William last November.
The 29-year-old used red accessories to finish off the look. Her hat by her favourite milliner Sylvia Fletcher at Lock & Co, featured Canada's national symbol, the maple leaf, as did her diamond brooch, which was borrowed from the Queen.
But this particular outfit pays special tribute to the Queen, who herself gave a favourite white dress a Canadian twist around this time last year.
And the diamond maple brooch, which was first worn by the Queen on a trip to Canada in 1951, and again when she celebrated Canada Day in London last year, also references the Monarch.
Catherine's look has won praise from fashion press in the U.S. and Canada since the Royal couple arrived in Ottawa yesterday.
TV fashion expert Louise Roe, who hosts Plain Jane, told MailOnline: This outfit is such a home-run, for multiple reasons. First up, she's diplomatically - and stylishly - paying respect to Canada with their national colours and the maple leaf motif on her fab headpiece.
'Secondly, the recessionista princess strikes again! Re-using old clothes not only makes her more relatable, but the fact that it's the very same dress she won Britain's heart in, reminds us of why we love her.
'A very clever, calculated move, this look will have been carefully picked out long ago, head to toe.
'The only gripe I have is with the shoes. As a stylist I'd say too much red in the look! A nude or taupe patent pump would have looked better, and one with a higher heel. She's too young and stunning to wear mediocre kitten heels. Somebody introduce her to Jimmy Choo!'
Lauren Sherman, Executive Editor of Fashionista.com, who regularly covers the Duchess's style, also had praise for the look.
'I love that she's wearing the Reiss dress again,' she said. 'I think her look is very Eighties aristocrat, but in a good way. The matching shoes and hat are a little silly, but finally show that she's willing to take a few risks.'
'As for her legs - is she wearing nude tights, a la Pippa? I say those have to go, or she needs to lay off on the self-tanner.'
The Duchess's wardrobe meanwhile, continues to be a source of fascination as she scored a sartorial hat trick yesterday, changing outfits three times.
To board the plane to Canada, Catherine wore an elegant navy Roland Mouret dress and Smythe blazer but changed mid-flight into a lace design by British-based, Montreal-born designer Erdem Moralioglu.
Later in the day, she changed into a bird-print dress by one of her favourite designers, Issa, for dinner with 120 of the cream of Canadian youth at the Governor-General's 175 room mansion, Rideau Hall.
The young prince and his wife have star power to burn and Canadian Heritage Minister James Moore reckons this will be one will be the most-watched royal tours in Canada's history.
Source : Daily Mail.co.uk