I use a 500mm manual lens on my DSLR for mostly for wildlife. It is a bit of a pain, but the images are worth it. There are quite a few M42 adapters made for various cameras, Canon being one of them. Some have "chips" built in to tell the camera that a lens is mounted. There are also adapters for other lens types available. I have an adapter that allows me to use my old Minolta MD extension tubes, bellows and lenses on EOS bodies.
You won't find much difference than the old "match the needle" metering of the Spotmatic except for the lack of automatic "Stop Down". I forget that at times and end up with real off exposures