We were only there for 5 days so we just got the daily Talk+Text+Data for $4.95/day but it seems as though it would be more cost effective for you to get the monthly plan. ($84.15/17 days vs $64.95/month). We bought the SIM cards at London Drugs, I think they were $15/2 and we have used them for 2 years now.
Depending on your cell phone provider, it might be more cost effective to use their roam plan. Telus has a $7/day plan that gives you access to your Canadian plan. We used this option for our August trip for my phone since it was a new phone that is not unlocked. Unlocking costs $50/phone right now so it was not worth it to us to unlock mine. We used the Roam SIM for my husband and the Telus roaming for me.