Anecdotal of course, but anti-American sentiment was definitely high during the Bush years and then came way down when Obama was elected. I don't think Canada is some special case of this, rather just a reflection of the typical world view on the US.
The Anti-American sentiment has been around forever, it definitely cycles with current administration or level of stupidity take your pick. During the Bush era at an NHL game the American anthem was booed from start to finish and people would refuse to stand. Then they would fucking belt out Oh Canada at the top of their lungs. That all stopped with Obama and some sanity appeared to return.