I did the same a few weeks back and used an Orange PAYG Sim. They charged me 5 UK Pounds for the data charge for a month.
There may be better options with Vodafone or T-Mobile but Orange worked OK for me.
Make sure you get a 3G Sim card.
You may find that your Canadian BB may not have the same channels as those used in the UK and Europe so it will step down to the common denominator (potentially slower).