I've used quite a bit of Rafter S leather as they have virtually no cant whatsoever.
Rafter S Gunleather
Most custom makers will build a holster without a cant if you want.
Galco has the "Avenger" model which has no cant at all.
Most of the plastic holster have no real cant (Uncle Mikes, Blackhawk, etc.) or are adjustable. If you're into Kydex, try Blade-Tech or Comp-Tac. Good companies.
Depending on how large your firearm is, I've found that it is much easier to draw a larger firearm (say, a Beretta 92, 1911, etc.) from a slightly forward canted holster. Smaller frames are much easier to draw from a vertical cant.
Canted holsters are designed to be worn around the 4 or 5 o'clock position which affords a much more natural draw stroke. Where are you wearing your holster?