Exactly. This only affects Canada, and even then not overly profoundly. An earlier rail link to the coast is a huge windfall for the tiny port of St. John and it might get as big as Halifax and rival the main city of the Maritimes. The other thing that changes is that with its economy now firmly tied to Canada, it could potentially spur a slightly earlier Confederation, or less opposition to it, as Nova Scotia might feel more locked out of a greater economic union while New Brunswick reaps the benefit.Generally this is my thought as well, and save for the Montreal to St. John rail line actually being built and having an ice free port sooner. Now that changes some things for Canada when it comes to Confederation, but for the US I'm not sure how much really changes overall unless there's other territorial concessions elsewhere.
There are always butterflies, but due to demographics and geography Canada has a pretty clear trajectory for most of the 19th century and I don't think this does enough to change those.