Title doesn't relate to your post.

Due to my experience sooner you start to get job experience sooner you achieve higher income. So internship will give you this experience. If it's possible to have it while learning? Due to your timetable. But in general you'll get much more useful skills from internship than from grad school..

Pink, there is a great deal in your post.  Let me try and summaries in a concise manner. Full disclosure, I am a licensed architect in Ontario with degrees from both Carleton and Waterloo.

1. UofT is NOT an architecture undergrad.  Do not consider it, even if it is your only option.  You're better off taking a completely unrelated bacherlor degree then apply to a 3-year M.arch elsewhere.  On the other hand, Waterloo is without argument the best undergrad school in Canada and will easily set you up for practice and entrance into any M.arch. Don't think about M.arch schools just yet. Wait until you get your feet wet in the profession to decide your grad direction.  It gets complicated depending on where you want to eventually work.
2. How do I do it?  I worked my ass off where (not when) it mattered. Undergrad studio is difficult and very time consuming.  You need military style discipline and the ability to make confident decisions... and enough artistic flair to keep things fresh and interesting.
3. Money?  Why bother? Tuition is dirt cheap in Canada compared to the US or elsewhere with international fees.  You should be able to cover tuition with a minimum wage job in your last year of high school and summers.  The rest of the cost is handled through OSAP (if studying in Ontario).  Note that unless you're a super star, you will not have much free time for part-time work while in undergrad.  I worked 25hr part time in retail while handling 60+hr studio workloads in the first half of my undergrad, then 2 days/week in a small architecture office in the second half. See point 2 above for time management skill requirement.  While in architecture school, your design studios take up all of your time including evenings and weekends... sometimes from the very first day of class.  Side note, most universities have COOP options.  Waterloo has the better one and is mandatory for graduation. You get paid for COOP.
4. Working without pay is dumb and you should hate yourself for considering it.  Some countries still enjoy this type of slavery (Japan being one) but it is an absolutely disgusting practice.  I would not hire you if I knew you valued your time so little that you accepted work for no pay.  With that said, in canada, your internship period does not start until after you finish your M.arch.  You can still work in an office, but those hours will not count towards your minimums... and those are minimum hours spread over a dozen categories, not a blank "work X years" deal.  Minimum is 3years but most take 5 to 10 because not every office is set up in a way that allows junior staff access to all phases of the practice.  I completed mine (older program with almost twice the req hours) in just under 3years.

Good luck and don't apply to UofT undergrad.  Literally every other school in canada is better and if you live in the GTA, you have no excuse not to apply to Waterloo.  Just remember that you have no chance at succeeding if you think you can live in Toronto and study at Waterloo without moving to Cambridge.  No chance.

As for if architecture is the right choice for you... we can't really help you out with that.  Do you love buildings and designing spaces? Do you love figuring out how things go together? Are you fascinated with construction and assembly details? Do you have a portfolio started?