Who was responsible for stopping Americans from winning Canada?

The British Army was responsible for stopping Americans from winning Canada.

Explanation:

The plans that the United States government had of invading Canada were intelligently devised by the British well in advance. When the US Army marched to invade Canada, it was confronted by British army troops. Though the war between the British and the Americans ended with a peace treaty, it was only because of the retaliation posed by the British that the US Army backed out.