On T-mobile you can get as low as $0.15 per minute, or as low as $0.06/minute once you become "gold". You are "gold" after adding $250 in topup credit.
If you are gold and add $100 to the account you'll get 665 minutes + 1000 bonus minutes.
Canada will ALWAYS Cost you $0.40, and I don't think there is a single plan, pre OR postpaid that can change that.