There still is, kind of. It is usually much easier to be granted a US non-immigrant visa when you are already a Canadian PR. Not always (I've read of one denial on this forum), but in most cases.
I believe US visas were waived for Canadian PRs before, but the visa requirement was reinstated for non-visa-exempt passports, so now a Canadian PR with a passport from a non-visa-exempt country will still have to apply for a US visa for formality's sake.