You are going to choose a lens primarily for filming with. With this in mid it is useful to have a fast lens that can utilise a wide aperture, at least f2.8.
A wide aperture allows you to shoot in low light and also to control the depth of field and what part of the image is in focus and what in the frame is blurred. The allows you to direct the viewers gaze at what you are highlighting in your shots.
There are a vast number of choices for Canon lenses from around £80 to £1000’s of pounds. I have selected a few fixed lenses that have wide apertures that will be useful for filming in low light.
Another useful feature to consider is anti shake features, image stabilisation, that can make hand held video much smoother. These are much more expensive.
Some of the 50mm lenses offer a decent compromise for some landscape and also portrait work at a much cheaper price point.
Useful sites to look at:
The Wide Angle Lenses used particularly for capturing landscapes can be very expensive as the glass is usually of a very high quality.
Looking at what Canon enthusiasts are saying a good compromise lens with a constant f2.8, across its range, which is very important, is the 17mm-55/ f2.8
It is not an l lens from Canon but not far off that quality. I think you should have a look at it Ali!