Final answer:
Ontario and Quebec probably gained the most from joining Confederation in 1867 due to political stability and economic integration, while maritime provinces like New Brunswick and Nova Scotia may have felt they gained less. West Virginia's formation during the Civil War, though not related to Canadian Confederation, embodies a state gaining from secession based on ideological differences.
Step-by-step explanation:
The question of which colony gained the most or least by joining the Confederation in 1867 involves assessing the political, economic, and strategic benefits or drawbacks experienced by the provinces. Among the provinces that joined Confederation in 1867, Ontario and Quebec (initially as part of the Province of Canada) likely gained significantly due to increased political stability and economic opportunities within a larger national market. Comparatively, provinces like New Brunswick and Nova Scotia may have perceived they gained less, initially, due to concerns over losing regional autonomy and the economic uncertainty of aligning closer with the Canadian interior rather than maintaining their established maritime-centric trade relations.
There's also a unique case in the formation of West Virginia, which, while not part of Canadian Confederation, resulted from similar secession dynamics during the American Civil War as it broke away from Virginia due to deep opposition to secession and slavery, forming a new state that joined the Union in 1863.