If you can get both, much better. If not...

- for the City, i'd say back up sensors would give good coverage. It's a subcompact with a short back. Your rear view and side mirrors should be able to give you a good view already.

- for the Fortuner, IIRC autobisyo has backup cameras for the fortuner. Look autobisyo/jlmedes up. For this i wud prefer a backup camera because it's a bigger and longer ride with more blindspots, esp at the back. I'm not fond of a rear underview mirror for a midsize suv.

I like the comment about not merely relying on technology. It does help a lot but it also is a judgment call at times. Don't be lazy and also go down and have a look around if the situation allows you safely to do so.
o the T