It is possible to do your LLB in the UK and write your NCA exams (the number you have to write is determined by the NCA), then write the Bar exam and get a firm to take you on for articling. You can also study a version of the LLM at some law schools, like Osgoode for example, that satisfies the NCA exam requirement. (People sometimes take this option because it gives you access to the universities' career services which can be great)
Remember that the biggest hurdle will be getting into a firm to do your articling. Canada has relatively few law schools and the legal market is very competitive, especially if you've been educated at a foreign university (other than Oxbridge). There can be a perception that Canadian students go to law school in the UK because they couldn't get into a Canadian school. It depends on what type of law you want to practice, but if you're aiming for top commercial firms in Toronto, for instance, you will be competing with local graduates who managed those 7 years without 'burning out'.
I don't mention this to stress you out - like others have said, many do it and it is certainly a viable path. Just try to keep in mind who your competition will be when you do head back to Canada and try to use the next few years to make yourself as competitive an applicant as possible. There are plenty of Canadian law students in the UK who are naive about this, don't be one of them.