In the War of 1812, we invaded Canada. Was that the reason why we went to war with Britain?
The desire to invade Canada is not usually seen as a major cause of the War of 1812. However, there were certainly some elements of US society that wanted the war so as to be able to invade Canada.
The main causes of the war were the British infringments of US rights. This included things like the impressment of US sailors and the fact that the British were helping Indians attack Americans in the Midwest. However, there were the "War Hawks" who did want to invade Canada. This was partly out of a desire for more land into which to expand, but it was also partly because they wanted to stop the British in Canada from inciting Indian attacks.
So, the desire to invade Canada was a partial cause of the war, but it is not typically seen as the most important cause.