There were many reasons the invasion of Canada was a bad idea, but for the experienced commanders the core issues were logistical. The terrain vastly supported the defending Canadians, supplies were hard to move through the countryside, and the brutal Canadian winters meant delays could be deadly. None of which changed the fact that Horatio Gates wanted to conquer Canada. I have to assume he wanted to build a gigantic ice fortress and plan his conquest of Iceland and Scandinavia in it.