Well assuming this is possible (and I'm of the firm opinion it is not) then you have a very interesting problem for Canada. The first is clearly that it is now without a access to a warm-water port of its own (the northern St. Lawrence as it empties out into the Atlantic remains iced over from roughly December 5th to May 5th, sixth months of the year) and so remains dependent on US rail lines and ports. Now this either leads to Britain having an increased presence on the Pacific Coast (to prevent the Americans from dominating it) and an earlier 'trans-continental railroad' to connect Canada and BC, or it leads to a very slow absorption by the US of Canada.
It would really depend on the economics, Anglo-American relations, and so forth, but in this scenario I definitely see eventual absorption of Canada into the US as a much higher probability than full on Canadian independence.