Simply put, if you're ineligible for any ancestral visa, the quickest way would be to marry a British Citizen. That way you are eligible for ILR after 2 years, and citizenship just one year later. The other option is the Tier 1 Entrepreneur visa, but you need at least £50k, and you can only work for yourself (details here: https://www.gov.uk/tier-1-entrepreneur)
I trust you're aware of the restrictions of your visa, especially the "you can't extend your stay" bit, but just in case there's a nice overview here: https://www.gov.uk/tier-5-youth-mobility/overview
I took the marriage route and I've been in the UK for 5 years, and eligible for citizenship for about 2 years, but home ownership and general apathy are finding other uses for the exorbitant fees over £1000. I'll definitely do it eventually, but the only immediate benefit I can come up with would be getting through the passport queues more quickly when travelling around Europe. I have always travelled on a Canadian passport and I've never had a problem.
Commonwealth citizenship isn't worth much, it pretty much just grants you the right to vote in local and national elections, but you're excluded from voting in European Parliament elections. You might get a more favourable reaction from UKIP or BNP supporters because you're the "right kind" of foreigner, but even that's iffy.
As a Canadian, you're also eligible to swap your driving licence like-for-like, except it'll be automatic only. To drive a manual car you'll have to take a full road test like any other learner driver, but you're exempt from the theory test. These can take a long time to arrange, mine took 3 months!
As I said, I've been here 5 years and I'm struggling to think of more than that. The rules are pretty clear, just follow them to the letter. If the forms say use black ink, use black ink. If they want 3 copies, don't assume that 2 is enough, that type of thing.
The only other thing I can recommend is, if you're serious about this, changing all your bills to paper copies through the post. Do this ASAP. I know what it sounds like, but despite it being 2015 and emailed bills being the norm rather than the exception, the Home Office still prefer paper, but only if it's official. Printing something yourself will simply not do. I think we'll continue to get paper copies until after my wife gets Canadian citizenship after we possibly eventually move back to Canada at some point in the distant future.
