Its opening a full on current account that is so hard. If you don't need an overdraft then you can get an account with The Co-operative Account called the Cashminder relatively easy. You will need a permanent address and a way to prove that. A lease will work.
If you are coming here with a job offer, then a good company would help you open a full on current account with the bank which does their corporate bank accounts. Speak to someone in HR or even your accounts department if the support is not offered up front.
Before you leave find out who your current Canadian bank uses as its correspondent bank in the UK. A reference letter from one to the other will help immensely. If you bank with a credit union, there are now some credit unions here in the
UK which offer proper bank accounts. You can find more information at the ABCUL org website . If there isn't a suitable credit union for you, head for The Co-operative Bank