In the U.S., the majority of soft drinks are sweetened with high fructose corn syrup, rather than sugar. This change seems to have been made in the late 1970s/early 1980s... some even speculate that part of the New Coke rollout/disaster and return to the Classic Coke formula was to implement HCFS. (I'm not sure about that rumor!
)
Canada, as far as I know, still sticks with sugar as the primary sweetener, thus Dr Pepper should taste pretty much the way it was intended.
I wrote a little about the whole HCFS vs. Sugar battle when I reviewed
Kosher for Passover Coke a few years back (yes, I know it's a silly name for a drink... but it sure is tasty!)