What lens mount does this lens have? Also how cheap/easy would it be to buy/make an adapter to adapt this lens to Canon EF mount?
in case you can't read it, it says EBC X-FUJINON-T and 1:3.5 f=135mm DM on the front ring of the lens.
X-Fujinon says it all - that's Fujica X-mount, the one Fuji used on their SLR cameras from the early 1980s, before current mirrorless X-mount.
Fujica X-mount has focal flange depth of 43.5mm, so there is no way to effectively use this lens on Canon EF-mount body since EF-mount had bigger focal flange depth of 44mm - there is no way to achieve focus to infinity. On the other hand, you could remove the current mount, grind down a lens for 0.5mm, add an EF-mount onto it, possibly removing the aperture lever in the process, those levers are known for getting stuck on a mirror on Canon full-frame DSLRs. If you have an access to machinery needed for that, I'd say go for it, document the process and put it on the internet for future generations.
Also, you can use that lens on any mirrorless camera with just a simple, cheap adapter available almost everywhere.