For tips on travel sims I always check out http://prepaid-data-sim-card.wikia.com/wiki/Prepaid_SIM_with_data
I have a few I keep active but have had single country sims from around the globe for various trips.
For in Canada, SpeakOut from 7-11 works well, but watch the $1.25 monthly 911 fee. A better deal can be a tablet plan - best deal is data share tablet plan - $10 add-on to an existing smartphone plan to share the data (though you need an existing plan to share). You can often gets sims through apple store or via the discount brands vs main brand - i.e. virgin or koodo vs bell or telus.
Finally, for UK big fan of giffgaff, but even better is this site: http://giffgaffgsimabroad.wufoo.com/forms/z1mcn5md0w6bzvq/ that will ship your sim to US/Canada.
Re unlocked phones - usually $50 to get our iphone unlocked via carrier. Androids can be done in many malls. IF you only want text (i.e. no data) - old blackberries can be unlocked online for free or the https://www.roammobility.com/breeze-phone is $50 new.