Canadian English should not be described as a mixture of American and British English with an insignificant number of Canadianisms added. Canadian English, like all ‘Englishes’, possesses an important characteristic, referred to as wholesale borrowing, which has allowed it to develop a very rich vocabulary. Canadians have in the past and will most likely in the future continue to borrow freely from both American and British English; however, once a lexeme is borrowed, it has the possibility to evolve differently. In other words, Canadians appropriate it to suit their needs. The lexeme chesterfield
is a par exemplar.
According to Robert Hendrickson in the Encyclopedia of word and phrase origins, the term chesterfield is commonly applied to a sofa in honor of Philip Stanhope, the forth earl of chesterfield (1694-1773). However, Hendrickson points out that it is more likely that a latter earl of chesterfield invented them, which earl he does not know.
At any rate, according to the OED, it was used to refer to a couch in 1900. According to Carver in American Regional Dialects the term appears to have come into use in Canada around 1903 and in Northern California about the same time. The Jrnl. Canadian Linguistics Association (qtd. in OED) notes chesterfield seems to be in general use throughout Canada, though the usual American sofa is also known and used.
Almost everywhere in the U.S chesterfields are cigarettes and nothing more.
In Great Britain, a davenport couch was sometimes referred to as a chesterfield but this is obsolete.
The point to be taken is that since chesterfield has entered Canadian English it has evolved differently because Canadians have appropriated it to suit their own needs. To be sure, although chesterfield is not originally Canadian, it is thought of as such by Canadians because Canadians commonly use the word to refer to a sofa or couch, while the American and British do not, save maybe the region of Northern California in America.