In 1968, there were indeed 3 types of Canadian dimes, but none were 90% silver. Canada didn't make 90% silver coins for circulation, they were 92.5% (sterling) until 1920, then reduced to 80%, until mid-1967 when they were reduced once again to 50%.
The 3 types in 1968 are: 50% silver, 99.9% nickel minted in Ottawa, and 99.9% nickel minted in Philadelphia. You can tell the Canadian made nickel dimes from the U.S. made by looking at the reeding. The Canadian dimes have V-shaped reeding, whereas the U.S. minted dimes have flat-bottomed reeding.
Scott