I think the comparison with Cantona and Zidane is an interesting one because it's one of those, where, on the face of their career accomplishments alone, you're going to get a lot of "nowhere near as talented/good" sort of comments. Cantona was also the biggest French all-round attacking talent in between platini and Zizou ( Papin being an out and out goalscoring 9), the one with arguably most expectations for a widely internationally recognised great career, so the comparison is quite direct to see why one fulfilled that, and the other fell slightly short , outside of being considered one of the better players in his position for his generation/a certain league.
personally, i think the gap as far as individual talent/pure footballing ability go is marginal and not the biggest difference in why one ended with a career that can be accurately said to be a couple of levels below. Both had great technique, vision and intelligent tactical interpretation within a well set positional role ( supporting forward for Cantona, attacking/creative midfielder for Zidane) and didn't step too far outside what was expected from the typical elite player in their positions. Each have some advantages over the other, and some similar weaknesses like average pace/defensive application.
Difference in personal character clearly played a big part; Cantona a serial troublemaker in his French career, despite being recognised by the likes of Platini as a great talent and potential successor as team leader, he obviously needed more specific club/manager/teammate circumstances to settle and play to his best.
Then choices of leagues/clubs: Cantona should have gone to Italy (or even Spain) if he was being entirely career minded, even a mid table club at first. Getting then suceeding in the best move at the right time is vital for piling up the team accolades and transcending your era( in the eyes of type of fans who will rank players all-time at least) and plenty of potential greats don't manage it, especially back pre-00s. Cantona finds himself in a league/club that has great history, but currently relatively fallen from grace; even with the romanticism of bringing a big club like united back to the top domestically, it's tougher to be recognised as among the very best in the world from the top of early-mid 90s post-ban England than Italy, unless you can win a few times in Europe, which foreign rules could make tough for certain leagues. Zidane would not had have got the same acclaim playing the same way for Blackburn or Newcastle -had they the foresight to see his talent instead of rejecting him - or even united, as he did for Juventus. Once you made it at Juve or Milan in the 90s, that was you in the best possible position to maximise your talent, with trophies and international recognition from playing in the best league. A sidestep move to Real or Barca, as Spanish football eventually caught up with Italian was well set up, and the trophies will keep flowing.
Internationally, both have lots of talent around them, but Zidane's era went a step further there overall, and maintained a more cohesive core/style, while Cantona's was initially transitional and underachieved. Cantona generally played very well for France imo. He was prolific and creative, but when he had a period of bad form like most of the Euro92 group stage, the rest of the team had also too many players underperforming as a collective, and didn't manage to compensate so he could get back in form. Zidane had a better contributions from teammates when he wasn't there, or playing badly ( 98 last 16, 06 group stage) I strongly suspect the 06 French team would have gone out right away, if they had been against some of the stronger opponents that notably foiled the Cantona era like 89-90 yugoslavia, 92-94 Sweden, 92 Demnark, Stoichkov/Balakov era Bulgaria...They also came very close to not qualifying, or at least being forced into a playoff for Euro 2000. So Zidane's era also just had some of the fine margin fortune you need in international football when playing under form.
tldr; when comparing zidane and cantona's careers, i think it's ultimately different team, league and character factors that make the real difference in ranking, rather than a substantial gap in talent.