And the reason they had to be transported by sled, sleighs and carts to the railroad was because the east end of the canadian railroad used tracks thru the state of Maine to get to the Atlantic...the british couldnt exactly transport troops thru the country they were being sent to oppose.
"....when the british troops arrived, the St Lawrence was already frozen over, and the only railway link to Canada was on American soil through Portland, Maine... The need to undertake a winter trek overland in sleighs through New Brunswick demonstrated the strategic value of the proposed intercolonial railway and prompted the British government to reconsider its commitment to colonial defense."
p. 171, A Brief History of Canada
, by Roger Riendeau
The reason England feared american attacks on Canada is the answer to the other question.