I don't understand your idea that London is the only city in the UK either. Are your jobs so specialised that they can only be done in London? Really? Not Bristol, Exeter, Nottingham, Manchester, Newcastle, Cardiff or Edinburgh? You can find lovely communities, schools and teenagers all over the place if that's what you want.
On Canada, my parents came here from there (London was considered quite excting in the 60s. They then settled in a lovely northern town), I've visited many times and my younger half-siblings grew up there.
Some scattered thoughts:
Teenagers can be crap everywhere. I once travelled by bus from Vancouver to Ottawa and everywhere, especially the small places with the most intriguing names (Medicine Hat, Moose Jaw) the one consistent feature was the 'bored bus stop kids' just hanging about, exactly as they do in every town and village in the UK.
My own observation has always been that Canadian kids are very self-confident and talk in a very equal way to adults, though, especially when a (reserved British) teenager myself, I've sometimes wondered what it is that they have to be so self-confident about - healthy self-esteem perhaps bordering on bumptious entitlement.
There is a more egalitarian, meritocratic, pragmatic society there. Less of the tradition, red-tape and class-based 'who you know' networks that still affect some fields of work and life here.
Society generally is also more right-wing, economically if not always socially, taking what we'd see as Tory ideas about free markets, enterprise and self-reliance completely for granted so that everything is very commercial, and viewing what we'd see as mainstream left of centre as raging socialism. It's a lovely place to be if you're well-off but you wouldn't want to have to fall back on state support in any way.
Schools and health provision are generally very good though and hardly anyone goes to private schools, which contributes to making the state schools good and, as people just seem to go to the nearest one, much more dependent on their neighbourhood for general standards. Secondary education is more broad-based, less specialised, so the school-leaving standard is lower, university takes longer and you have to pay for it, though that's no longer a difference.
There is an odd cultural mix between brash, commercial, uber-confident American and repressive Scottish protestant (early eastern settlers), so that films on TV can have endless violence but no nudity and alcohol can only be bought from government-run liquor stores and was wrapped in anonymous brown paper bags until about 15 years ago.
I once asked my brother whether he'd ever regretted or even thought about growing up there rather than here. He looked quite horrified and said no and why would he since he was able to grow up skiing (including at school, like swimming lessons) and spending summer weekends at people?s lakeside cottages, as if wanting to be in the UK was the most ridiculous idea ever.
Think about how you'll cope with long winters at -10 to -20, followed by a long, muddy, grotty thaw. Toronto isn't the coldest place, but will be gloomy and cold in winter.
How's your French? If you work in the public sector you will have to undertake to improve it and, above a certain level, will have to be able to work in both official languages.
The eastern side is only seven hours or so from here and there is a low cost airline with rtn flights for approx £500 rather than £750 on AC or BA. So, if you have the money, you can get back in an emergency.
The things I always notice on coming back to the UK are (in summer) how green it is compared to their wilted foliage but with so little urban green-space and how much dog shit there is everywhere ? Canadians have picked up consciencously for years.
I'd agree with trying it for a year, there's so much you won't know until you get there.