As I stated before, one of the reasons for confederation was a need for railroads. There were many obstacles separating the United Province of Canada from the Atlantic colonies. Some of these obstacles were the Gaspé mountains, the U.S. state of Maine, and the St. Lawrence freezing in the winter. A linked railway would be useful to the colonies because it would increase trade and move troops more quickly. Colonies were going bankrupt trying to build their own railroads and joining together would allow them to share the costs of a linked railway.
Another reason for the Confederation of Canada was the threat of American expansion. The colonies were afraid of American invasion and they thought if they joined together they could defend themselves better. There were 5 key pressure points where American invasion was feared. One of the pressure points was British Columbia. This was a pressure point because of all the American miners that had moved there during the Gold Rush. Another reason the colonies were afraid of American invasion was because of the fact that Americans believed in Manifest Destiny.
Lastly was the desire to expand settlement west. The majority of the good, fertile farmland up to Canada West had already been claimed. Settlers were looking to the west as possible areas to settle. Americans were also looking to settle the west as well. The colonies thought that if they joined together they could annex the west before the Americans did.
So as you can see there were many good reasons for the Confederation of Canada. Three of them were a need for railroads, the threat of American invasion and the desire to expand settlement west.