You don't need a great average for architecture programs, bar McGill. As long as you have a decent average (80+ for Ryerson and Carleton, and 85+ for Waterloo) you should be okay. You'd probably need a 90+ for McGill though. The other stuff (evaluations) make up the rest. I was considering Architecture earlier this year, and I applied to Waterloo and Ryerson. I was rejected from Waterloo but received an offer to Ryerson in one of the early rounds, so if you wanna gun for Waterloo, what I have to say might not be too valuable.

I'm not too sure about the out-of-province admission system, but I'd say you're lucky for doing the mail-in portfolio. You have to do a sketching exercise at Ryerson, and a writing exercise at Waterloo. Doesn't seem like you're all too comfortable with either. You can have pretty much anything in your portfolio for every school. As long as you're displaying creativity, skill, etc. My portfolio was predominantly based on paintings, personally. I had a couple of sketches and one 3-D model, but no heavy design or photographs. You need a decent amount of pieces. I know people who had up to fifty, I personally had eight.

You need to start working on your portfolio now. There are people who have been working on them for years already, applying to the same programs. Pieces in my portfolio were up to 4 years old. You need to be really committed and work really hard, don't half-ass your pieces. There's no real way to get in without presenting a well-done portfolio. That being said, its probably not as hard as you make it out to be. I know Waterloo is very competitive, but I have lots of friends who made it to Ryerson. Not too sure about Carleton though.

Each school has a different process. I know that Waterloo requires you to talk about three of your pieces in a recorded video. Not too sure about others, you're going to have to do your own research on them.

you don't need THAT great an average to get into architecture. The portfolio and interview count for at least half of the admission considerations.People got in McGill with an average barely over 90, something like 90.2. But I know people with averages like 95 being rejected. Once again, the difference is in the portfolio.
I know for Waterloo you just present your original pieces and talk about it (if you choose to do the in-person interview). And Carleton and Ryerson are somewhat easier to get in. However, if you are considering McGill, then you need to worry about not only what you have in your portfolio, but also how you present it. Basically you have to design a book that shows off all your pieces (they won't take originals). Try use softwares like InDesign. The design of the portfolio matters as much as the content itself.
And yes, start working on your portfolio now! It might already be a bit late. 3D models, graphic designs, and photography are great to include in the portfolios. Imagine if you are the admissions panel. You go through portfolios after portfolios of beautiful drawings. Wouldn't you get bored? The point is to show your creativity and orignality in ways that capture their attention and stand out.
Lastly,ask yourself if you really want to study architecture. It's one of the hardest programs in university and the pay afterwards is moderate at best, provide you can find a job.

well, you better be prepared because in architecture, EVERYTHING requires a portfolio. It takes a portfolio to get in. It takes a portfolio to graduate. And it takes a portfolio to find a job afterwards. Any architecture program that does NOT require a portfolio should be taken with a grain of salt.

I don't think architectural technology is a good backup, unless you are hell-bent on doing architecture for the rest of your life. You have to know that a bachelor's in architecture won't make you an architect. The least required is a master's degree. So, if unfortunately you don't get in for bachelors, then try something different that you like. I know a landscape architect who studied liberal arts as his bachelor's. You can always try architecture again later when applying for masters. And who knows, maybe during those bachelor years you will find something else that you love more. And if you do still want to do architecture afterwards, then those extra years will give you time to do your portfolio.

And don't limit yourself to the traditional drawings, paintings,and things. Do include them. But be bold and creative. Anything goes. Someone got in McGill a couple of years ago with two wooden sculptures only and another guy got in with only photography. What I am saying is experiment. Looking back, I wish I had included more non-traditional stuff in my own portfolio. But I guess I was lucky that they were satisfied.

Finally, don't include building schematics and blueprints. That's practically suicide for your application.