Speakout Wireless (and I believe Petro Canada) don't require any monthly top-ups. You can buy a voucher that lasts a full year. With Speakout, adding any amount just before the year expires will also let you carry over any unused credits for another year. Rinse, repeat.

There are two kinds of pre-paid in Canada that I've seen, the flat monthly plan which is pretty much the same as the contact plans, and the pay-as-you-go. Speakout and Petro are PAYG. And no one in Canada does PAYG data. It's nearly impossible to find even low fixed price data, the exception being the iPad plans. Which no longer work on non-iPad devices.