Plastics match data:
Residency and Fellowship Match 78% match rate
CT match data:
Thoracic Surgery - The Match, National Resident Matching Program (under "2020 Thoracic surgery match results statistics report"). 77% US MD match rate for thoracic.
You can match to either program from general surgery. How easy it is depends on you as an applicant and where you are applying from. The other hard part is going through a general surgery residency and dealing with general surgery as a field if you know you are not genuinely interested in it at some level or if you would not be happy being a general surgeon if you didn't get a fellowship.
The integrated match tends to attract very high scoring applicants. If you have a poor step I/II etc. probably easier to match a fellowship than integrated residency.
As noted, they are vastly different fields despite some superficial similarities. Just because they are both 'competitive' and surgical, doesn't make them similar. Superficial similarities - filled with 'driven' personalities, can be high stress, can be thought of as 'creative', can require lots of technical skill.
Big differences - 1) Patient populations. CT has usually middle-age to elderly patients (outside of congenital) and you'll be spending lots of time in the ICU in fellowship and a variable amount of time in ICU depending on your attending practice (academic/private, thoracic only v. cardiac or combined...). Plastics definitely has a broad range of patient ages and presentations although non-academic practices skew towards a younger population than CT.
2) Patient concerns. Again, it depends on your ultimate practice type choice. However, CT will majority of the time be dealing with 'life or death' lesions/surgeries - cabg/valve/cancer, etc. Plastics can deal with life or death lesions - skin cancers - but it's a very different context. Non-surgical practice concerns probably play a bigger role in plastics than CT (ie, office decor and patient satisfaction and word of mouth referrals, etc.)
3) Complications - In CT, the patients tend to either get better or die. (In general surgery, they linger forever with drains and fistulas.....). In plastics, death isn't as common, but a really angry elective cosmetic surgery patient with a bad wound/implant infection can be unpleasant to deal with, too.
Would really recommend lots of exposure to both fields.