The correct answer to this open question is the following.
I think the colony which gained the most and the colony which gained the least by joining Confederation in 1867 were the following.
The most: the province of Canada that could benefit from the association with the other two for trade and relationships purposes.
The least: New Scotia, because the colony of New Scotia that had received the charter from King James VI. The chart was granted to Sir. William Alexander. It used to have relative stability alone.
On July 1, 1867, the colonies of New Scotia, Canada, and New Brunswick formed teh Confederation. These colonies officially formed the Dominion of Canada.