But if I may say so, that's a pretty innocuous gorwth of government power, relatively speaking. And one pretty arguably in the Constitution.
Especially given that without the transcontinental railroad, westward expansion would have significantly slowed and curtailed. Just as settlement of the Great akes would have been slowed or stymied without the Erie Canal, and southern settlement would have been stymied without federal intervention to displace the Cherokees and other Indian tribes.
In any case, the South's objection was not (save for a few bitter enders) to government promotion of a transcontinental railroad, as even you seem to recognize. What they hoped for was a southrn route, not a northern one - the main reason why then-Secretary of War Jefferson Davis marshalled through the Gadsden purchase in 1853.
As is so often the case, the argument over government largesse wasn't over curtailing it so much as to how to divvy it up.
The Erie Canal was a New York State project. I do not believe that the Federal government had any role in its financing, construction, or operation.
ML/NJ