Canonical is basically if "talented-kid-disorder" were a company. Canonical has smart people, but they're unable to actualize their vision.
They basically make the interview process extremely long to frame Canonical as some sort of prestigious institution. Not necessarily difficult or challenging, but long. If you really do your research, you find out that Redhat is far more profitable when Canonical isn't. Canonical's main selling point is that it's cheaper than Redhat. If you care about your sales career you'd want to sell for Redhat- which not only has a profitable product but has a simpler and faster interview process.
The process and the Glassdoor reviews are highly indicative of a strange circle-jerk culture where the employees think they are brilliant for being above average in high school.
TLDR: Canonical is a B player in the industry with an A player interview process. Don't be fooled.