Does the purchase go through with a fake (non-Canadian) credit card mailing address? Otherwise, borrow a friend's (non-Canadian) credit card and reimburse them? Are you running afoul of any taxation rules by doing this? Presumably Canadians aren't liable for Canadian GST when making online purchases outside Canada?

As for changing the IHG account address, it makes sense to have your account based in the US no matter where you actually live, because you will receive F&B certs valued at $20 apiece from your milestone choice rather than the significantly lower €15, ¥2000 etc. IHG isn't mailing you anything, so the address doesn't matter.

As for using points vs paying cash, sure, you have to consider the value of points earned and cashback. With good timing and stacking promos, you can earn 30%, sometimes more, on your stays.