Canadian leaders such as John A MacDonald were aware that the USA had expansionist tendencies.  MacDonald thought that the best way to prevent such expansion was for the remaining British colonies to unite into one "nation"

Description

Canada West--primarily English speaking, many were descendents of loyalists from the American Revolution. 

Canada East--originally the colony of New France until conquest by British in 1763.  Primarily French speaking

Nova Scotia--English maritime colony

New Brunswick--English maritime colony

Prince Edward Island

Newfoundland

Canada West and Canda East were mired in a situation where political progress was stymied by the government system.