I have an iphone 3G myself, I haven't looked into the plan because I'm busy getting ready to go back, but i doubt that you will need to use the phone provided by the providers. There should be some loophole or some "extra charge" you'll have to pay in order to use your own phone. My friends at Sim Lim have told me they have exported phones in bulk to Canada and I have seen Asian stores in Toronto selling the iPhone outright without a plan attached.
3G Wireless in North America is not as advance as Singapore or any other place that has used GSM technology for the last 2 decades. They've only made the switch to GSM in the last 5 years or so, many cell pones aren't even GSM yet. I wouldn't be surprised if you got blurry looks from a Canadian or American if you asked them if they knew about SIM cards.
Anyway, I doubt you will be able to buy a SIM card compatible with your iphone 3G. Most prepaid SIM cards do not support 3G wireless and your iphone needs a 3G sim card to operate. You can't even use a Singapore Hi! card or M card with an iphone. You would be better off purchasing a prepaid cell phone - they sell those at walmart and the cheapest one i've seen goes for about $20.
As for the HSBC account, if you open a HSBC account in Singapore with more than S$100,000, then go to Vancouver and go to a branch there, they will allow you to link both accounts. But it has to be over S$100,000. My dad has his account linked and I'm pretty sure he has over $100,000. My brother tried to link his Singapore HSBC account with his Canadian HSBC account, and being only 21 years old, he did not have $100k, so HSBC wouldn't link it for him. You might want to inquire at HSBC yourself. My uncle did the same thing when he sent his daughter off to UBC and he said the staff at HSBC were extremely helpful (although I think my uncle may quite possibly be a multimillionaire which is why they were so helpful).
Anyway now that you said you're landing in Vancouver, here's some information about the licensing that may help you out: http://www.icbc.com/driver-licensing/moving-bc/licence-othercountry#Variables._frag_
You have 90 days to convert your license in British Columbia, unlike 60 days for Ontario. I guess that gives you a bit more time to get your driving test done. Everything else seems to be the same as Ontario though.