Manual Pentax lenses can be used with non-Pentax DSLR camera bodies (such as Canon or Nikon) by making use of a suitable lens adapter.
What is a lens adapter? A lens adapter is a mechanical ring which allows the use of a lens on a camera body for which it was not designed.
Using such a lens adapter will facilitate the usage of manual Pentax lenses (all three generations) with Nikon, Canon, Sony, etc. DSLR camera bodies.
Amongst the Canon cameras, the EOS series is best suited for manual Pentax lenses.
Lens Adapters can be purchased based upon your combination of Pentax lens and DSLR body from vendors such as Amazon, eBay, CameraQuest, BHPhotoVideo, and so on.
For photographers looking to purchase a DSLR body to use with their collection of Pentax lenses, the following series of reviews may be useful: