No. It covers everything. You will only be charged for overages if you go over your regular plan allotments. It will max out at 100 dollars per billing cycle.
Vodafone currently has a "pay as you go 1" option where you can 1 pound a day for unlimited talk text, and 500MB. I used it recently in the UK for work and it worked great. It goes midnight to midnight. You can download an app like Fongo or use something like Skype or whatever you might prefer to have a Canadian number to call or be called back home that uses data.