What most affected the agreement between the united states and great britain over the canadian border

Neither the United States nor Great Britain were willing to start a new and expensive war.

This unwillingness brought bought countries to a negotiation table where the legal boundaries of Canada and United States were set.

These negotiations have been so successful that both countries have never had any territorial disputes in 200+ years.

Today, Canada and USA are part of the North American Free Trade Agreement have exemplary trade, economic and political relations.