UCL vs McGill UniversityWatch
Additionally, is McGill better in engineering/sciences?
McGill is really the most prestigous uni in its country but UCL probably is slightly more well known.
Its a negligable reputation difference overall.
For engineering, id imagine McGill is stronger UCL (at least in the UK) is not seen as a premier uni in the field.
But in other areas such as if you want to work in finance or consulting your probably better off at UCL...
For CS I am sure that UCL is better. Previously I thought you are talking about engineering or EEE, but for CS you can definitely choose UCL. If you want to stay at Canada in the future or you have considered a Master degree in the US, you can still hesitate and further do some research. Otherwise I suggest you choose UCL with no hesitation.
As an international student, I feel like it depends on your home country too (while both unis are great and reputable UCL is more well known in mine) and where you intend to relocate in the future if that affects you.