They're not all like that. I was engaged to a Canadian for awhile and he loved the US. He was a journalist for a pro-American paper in Toronto. He did love Canada, but also saw its warts. He completely understood that but for the freedom and protection of the US, Canada would not exist. He felt he had the best of both worlds and was eternally grateful to the US.
I think you hit a big part of the "Hate America" phenomenon right there.
Let's face it. We could take the place in a week. What have they got economically or militarily that could stop us?
On the other hand, they couldn't take the US over given the rest of eternity.
Personally, I think it's an inferiority complex. They have to yell and scream about how much better they are because they wish they were the top dog.
Hating America for no reason is a gutless choice.