I'm from Canada (Toronto) and have friends that have gone to McGill. My sister is also in law (though at UofT).
McGill is a very well respected school, and has a very strong law program. I can't comment on interships in London, but I agree studying abroad may may you stand out more, and McGill carries its own standard, from what I understand. Keeping in mind, I'm not a law student so I may not know the ins and outs.
Montreal is also an AMAZING city. You name it, Montreal has it. Great theatres, amazing food, great shopping, winter activities, great location for travelling... Weather might be a bit of a problem in winter (more snow and colder than you're used to) but I'm sure you could adjust. Montreal is one of the cultural centers of Canada so I'm sure it would really add to your uni experience. And most of the city is bilingual, so you should be able to get by with english (though it is true, some people may look down on you for not speaking french and speaking french is often appreciated).