If applying for a work permit from the UK it is EASY if you have the job offer first.
Do not apply for immigration through the UK though as it takes AGES and is an absolute pain in the proverbial rear end. The London office handles applications from all over Europe and is snowed under. Best to wait till you get to Canada and apply internally for landed residency. I have been told that is a lot quicker. I have been in the system over two years having applied through London and I am a valid controller over here and have a Canadian wife.....still being processed!!
And I have learned that pilots and the like are warmly welcomed here....no hostility whatsover. If you have come over with previous experience I have found that the Canadian respect that. Jobs like flying and in my case air traffic control gain a little bit more respect than if you wanted to open a chip shop!