I would reputation matters more in the UK than it does in Canada. The reason is all universities in Canada are like state schools in the US, most are somewhat obligated to accept a huge number of students, making acceptance rates and competition really nothing like what it is in the US.
Getting into uni in Canada requires only your top 6 Gr. 12 courses, no extracurriculars and your gr. 12 courses are not standardized either, meaning your teacher's grading is 100% of your mark, making the grades very variable from school to school and teacher to teacher. Acceptance rates for all schools and most programs is around the 60-70% mark and a few select programs at specific schools are highly competitive (Health Sciences at McMaster, Business Administration at Western (Ivey), Queens Commerce, Toronto Engineering Sciences etc) and some may look at extracurriculars or require essays.
So all in all, in Canada, no one cares about reputation, from a research standpoint, Toronto has more research funding than UCL, but it is also a much larger university and spread out. I personally would consider UCL more prestigious, but I believe in the states both schools will probably be similar in terms of prestige. Good luck with your decision.