It’s great to celebrate a little bit of Manhattan in London. The Hawksmoor makes a Manhattan with Bourbon, Vermouth, Maraschino, Angostura Bitters & a dash of Absinthe. It’s quite exciting because it comes on its own little tray with cherries and orange rind and a classic bottle. (In The Maltese Falcon, Sam Spade keeps one in his desk to help him think through particularly tricky cases). The Manhattan was probably invented at New York’s Manhattan Club in the 1870s, the Hawksmoor uses a recipe from 1892 which calls for a dash of Absinthe (which always makes their Manhattan just that more exciting).
Canadian whisky is often used in making a Manahattan – I’m not sure if this came about during prohibition, when whisky (Canadian Club) was smuggled from Southern Ontario into the US. Al Capone smuggled in thousands of cases of Canadian Club from Windsor to the US.