Public Mobile's pre-paid plans are for a duration of a 30 day cycle or 90 day cycle based on your choice. You can setup automatic payments so that the 30 day or 90 payment is debited from a credit card if that makes the payments easier for you. The phone plans do not have an expiry date and you can cancel at any time.
Here is a link to all the plans offered by Public Mobile:
PM does not have annual plan like some others. But not carriers have that these days
What is your budget? you can join the $15 /30 days plan, which works out to be $180 per year. You can 100 outbound minutes but unlimited inbound, and unlimited text and 250 Mb of data per 30 days. But this is a 30 days plan, ie, renewal every 30 days, and not annual plan which you pay once a year