I use my backup phone using a T-Mobile sim and their $2 daily plan with unlimited talk, text, and 2g data. To call and message back to Canada for "free" I use Google Voice and Google Talk.
Their $3 daily plan is the same as above but allows for 200MB (which I think is fine for 1 day) at 4G speeds. [I need to unlock my current phone before making use of this.]
http://prepaid-phones.t-mobile.com/p...ll-phone-plans
Correct me if I'm wrong but the equivalent Roam Mobility Plan is pricier $3.50/day but includes free calling to Canada.