In Canada people were working on the railway to make way money. It was also an easy way to make money. By them making this railroad it opened a lot of new things suck as markets and other regions coming together. The reciprosity treaty made Canada earn more profit by trading with the USA. They then thought that the reciprocity would help them get out of the depression that the corn laws put them in. This is how BNA colony were then united
Remember that it’s the termination of the Corn Laws and then the Reciprocity Treaty that led Canada to look for new trading partners. The railways created debt for the government that the other colonies could help pay off.