Cyfox,
If you could be more specific as to the which lens mount the Vivitar is fitted with that would be helpful.
If it has an Canon EF compatible lens mount it should fit without an adapter. A Canon EF lens mount looks like this or may be black plastic like the 18-55 kit lens that may have come with your T7 instead of stainless steel but the gold contacts will be there:
If it isn't a Canon EF lens mount but some other type, then it probably isn't worth the trouble and expense of tracking down an adapter. My recollection (from my Canon FD days) was that some of the Vivitar Series 1 lenses were good performers, but the lenses that were not Series 1 lenses were just OK. In any case, it probably won't autofocus on your camera even with an adapter if it doesn't have a Canon EF lens mount.
I have a T7 as well and a benefit to owning a T7 (or similar body) is that any Canon EF and EF-S mount lens ever made will probably work on the camera. If you're looking lenses, there are a lot of EF and EF-S lenses (Canon brand and other brands) that are available used and refurbished at very attractive prices from reputable sellers like the Canon Refurbished store, KEH.com, Bhphotovideo.com, Adorama.com, MPB.com, usedphotopro.com and elsewhere.
Good luck!
LZ
