Honestly the whole interview process is ridiculous if not preposterous and definetely extremely laborious for no reason at all. Application, written interview, aptitude assessment, interview, presentation etc. Its just ridiculous and its not worth investing your time and energy doing all that for such a company. My whole experience with canonical from the day i applied since thet day i was told that they wont be moving further my application was reflective what I heard in the industry about them. Bad management, unorganised and toxic. If you can notice those things from email interactions and interviews, you can imagine the situation phased by canonical employees. Lastly, keep in mind that they mostly take into consideration the aptitude assessment and if you are not perfect, they will immediately cut you.
I would strongly recommend staying away from this "company" and finding something different.