I have a T3 at the moment with a kit lens and a 70-300 Sigma. I'd like to get a prime and wide angle for landscapes.
Hello & welcome here.
* EF-S 24/2.8 STM
- brand new, very small, very light, dirt cheap, optically probably good but pending reviews, thanks to STM AF drive especially well suited for liveview and video operation; but serves APS-C sensors only, not suitable for "full frame" ... so in Nikon lingo it's a DX lens. :-)
* EF 24/2.8 IS
- excellent image quality, Image stabilizrer (IS = VR), reasonable price, compact, more than "good enough" build quality, lens hood needs to be paid extra; suitable for APS-C and full frame ["FX" lens]
if you want "real wide angle" on APS-C sensored DSLRs, there are basically 3 zooms to consider at reasonable price/performance levels
* EF-S 10-18 IS STM
- compact and light, decent IQ, Image stabilizer, STM AF drive, very good price/performance, APS-C only ["DX"]
* EF-S 10-22
- very good IQ (slightly better than 10-18), better build, decent price, APS-C only ["DX"]
* EF 16-35 / 4.0 L IS
- fairly new L-Zoom, L
uxury price, but excellent IQ, very good "pro" build quality, Image stabilizer, suitable also for full frame ["FX"]
All other Canon (ultra)wide-angle lenses 28mm and shorter either have poor image quality [especially all EF prime lenses other than 24/2.8 IS and 28/2.8 IS but also EF 17-40/4.0 L ... or are more expensive than optical quality warrants [namely EF 14/2.8 L] or are very large and without AF [namely tilt shift lenses, TSE-E 17/4, 24/3.5]
Welcome to Canon!