Hey!
I live in a city right next to Rotterdam (Schiedam, about 5km away from Rotterdam’s city center), so I know quite a bit about the city. The university itself is in the ‘rich’ part of the city, and mostly white people and students live there. You probably won’t ever visit the ‘multicultural’ parts of the city. You will also most likely be very safe. Crime rates are pretty low, and there have so far been no terrorist attacks or plans for these caught by the intelligence in this country.
And indeed, it is close to everywhere. You can ride the Thalys and get to Paris in 2,5 hours and Brussels in 2. There’s an airport in Rotterdam (an empty one, though) and you can get to London in an hour. Antwerp (Belgium) is an hour by train, and Amsterdam is an hour too. In the city itself you can get anywhere by bike.
Perhaps you should think about the prices too. A place to stay, tuition and food might be a lot cheaper in Rotterdam than in Toronto. And even though Erasmus might be lower on the list, it could boost your job chances in the future because a European university shows that you are not going for the ‘safe’ route, but would rather explore the possibilities (independent).