No, the merchant pays, although recently more and more have been handing off the 3% to the consumer by giving a lower cash price. But well, most people don't have cash so that's essentially a convenience fee.
Incidence is very much on customers, but (high interchange fee) credit card users are getting a rebate of most, if not all, of that. It’s the cash users who AREN’T getting a rebate, and thus the incidence is on them (and people using other low-or-zero cashback payment methods).