I will just point out few things that have been missed.
(1) The weather! Generally speaking, it's one of the worst. It can go down to -25C (less or more) in winter and stays at +30C in summer. In a single day, temperature can vary up to 20 degrees. So, if you are not familiar with such extreme weather, it can be a shock!
(2) People talk about racism in Canada, but to me, it prevails within all race/colour. When I lived in my home country Bangladesh, it's 99% local people, so there wasn't any chance to be racist

. But in Canada, it's full of immigrants resulting in hatred/empathy for each other to minimum/some extent.
(3) How happy you can be depends on what stage you start living in Canada. If you do high school and/or undergrad here; life will almost offer you same as a Canadian gets. But things are different for an immigrant who finished education and worked outside Canada (reasons are already given in earlier posts).
(4) Among US, Canada & Australia, I would put US first for education/job opportunities/income/growth. For peace of mind for a lifetime, Canada would be first. I would place Australia just at the bottom of Canada. FYI, I've been in all these countries.