I was shooting Canon professionally pre 1987.It was USM AF which was enabled by the all-electronic interface between the camera body and the lens that put Canon ahead of Nikon.
In 1987 when Canon introduced the EOS system, over 75% of professionals shooting in the 135 format used Nikon. Having said that, there were plenty of pros in the remaining 25% who shot Canon F1s. There were certainly pro-grade accessories available for the F1, such as high speed motor drives , as compared to consumer level lower speed power winders, and high capacity film magazines that could hold as much as 35 feet (250 frames) of bulk film.
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A scant five years later, in 1992, Canon had overtaken Nikon as the #1 camera used by working pros who shot 135 - there were still a ton of pros using 645 or larger format film.
Here is my F-1N with my FN-100 bulk film back, that I sold a couple of years ago (the back I still have the camera). It only took 100 exposures not the 250 of the earlier version but was useful non the less, particularly for 'remote' shooting (I had a 50' air remote release) where changing the roll of film wasn't practical.

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