https://books.google.ca/books?id=31A3GW76zKIC&pg=PA87&lpg=PA87&dq=Chretian%3A+%22I+have+to+tell+you+something.+I+don%27t+want+to+get+too+close+to+you.%22+He+looked+startled.+I+imagine+it+was+a+rare+thing+for+a+U.S.+Commander-in-chief+to+hear.&ots=6qWnsBOlr_&sig=ACfU3U0lXcxu5126--EkRQvKI95mBylLMw&hl=en#v=onepage&q=Chretian%3A+%22I+have+to+tell+you+something.+I+don%27t+want+to+get+too+close+to+you.%22+He+looked+startled.+I+imagine+it+was+a+rare+thing+for+a+U.S.+Commander-in-chief+to+hear.&f=false
This argument ignores all the early warning and defense systems installed in the north. Not like the US isn't the biggest part of NORAD and not like they wouldn't jump to Canada's aid if there were some attack.
Yeah, I honestly believe people forget just how steeped in American security Canada actually is. It does not need to be a state to be “protected”. I do not know where this idea comes from that America would just let Canada be invaded by anyone but them.